Chapter 31 Space Applications of Mass Spectrometry

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Chapter 31

Space Applications of Mass Spectrometry With contributions by

John H. Hoffman Physics Department School of Natural Sciences and Mathematics University of Texas at Dallas 800 W. Campbell Rd. EC 36 Richardson, TX 75080 (972) 883-2846

Thomas Limero Wyle Integrated Science and Engineering 1290 Hercules Drive, Suite 120 Houston, Texas 77058 (281) 483-7251

Timothy P. Griffin Material Science Lab (NE-L2) National Aeronautics and Space Admin. Kennedy Space Center, FL 32899 (321) 867-6755

C Richard Arkin Hazard & Gas Detection Lab (ASRC-14) ASRC Aerospace Corporation Kennedy Space Center, FL 32899 (321) 867-6758

Arkin, Griffin, Hoffman, Limero

Ch 31 — MS in Space

February 2010

TABLE OF CONTENTS

31

Space Applications for Mass Spectrometry .............................................................................. 3 31.1

Historical Space Applications for Mass Spectrometry ............................................................. 3

31.2

Leak Integrity Testing during Spacecraft Processing .............................:............................... 33

31.3

Real-time Leak Detection during Spacecraft Launch Activities ............................................ 39

31.4

Post-launch Analysis of Engine Performance and Integrity ................................................... 46

31.5

Gas Analyzers for Metabolic and Physiological Experiments ............................................... 52

31.6

Gas Chromatograph/Mass Spectrometry: Laboratory Operations .......................................... 60

31.7

In-flight Environmental Use of Mass Spectrometry and Complimentary Analyses .............. 72

31.8

Mass Spectrometers supporting Aerobee and Javelin Rockets ............................................... 96

31.9

Mass Spectrometers Supporting Explorer 31 Argo D-4 rocket flight and the ISIS Satellite Program................................................................................................................................... 97

31.10

Mass Spectrometers supporting Apollo Missions .............................................................:... 100

31.11

Supporting Atmosphere Explorer C, D, and E missions ...................................................... 104

31.12

Pioneer Venus Mission ......................................................................................................... 107

31.13

Mars Phoenix Mass Spectrometer ........................................................................................ 110

31.14

Reference Information .......................................................................................................... 114

31.15

Acronyms ..............................................................................................................................130

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ICh 31 — MS in Space

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31 SPACE APPLICATIONS FOR MASS SPECTROMETRY Mass spectrometers have been involved in essentially all aspects of space exploration. This chapter outlines some of these many uses. Mass spectrometers have not only helped to expand our knowledge and understanding of the world and solar system around us, they have helped to put man safely in space and expand our frontier. Mass spectrometry continues to prove to be a very reliable, robust, and flexible analytical instrument, ensuring that its use will continue to help aid our investigation of the universe and this small planet that we call home. 31.1 Historical Space Applications for Mass Spectrometry Provided here is a brief overview of mass spectrometry applications in the American space program and several specific case studies spanning the initial efforts in the 1950s through current day. 31.1.1 Planetary Exploration using Mass Spectrometers The first applications of mass spectrometry in space were carried out at the US Naval Research Laboratory in Washington DC in the late 1950's. To carry the instruments into space, the Aerobee rocket was developed for high altitude atmospheric and cosmic radiation research in the United States. [31.1.1 ] It was a small unguided suborbital sounding rocket powered by a single-stage liquid-fueled (nitric acid-analine) spin-stabilized rocket, which used a solid-propellant rocket motor as a booster. The first live-firing of an Aerobee occurred in November 1947, and by 1950 the Aerobee was in wide use by U.S. military research agencies. The original Aerobee carried a payload of 68 kg to an altitude of 120 km (75 miles). The nose cone containing the telemetry transmitter and the scientific payload was recoverable and returned to earth on a parachute. Many improvements were made in the Aerobee rocket over the next 10 years. The last of the variants was the Aerobee 150A. It carried 68 kg to an altitude of 270 km (168 mi). Extension sections attached below the nose cone contained scientific instrumentation. Ports allowed the instruments to "look out" normal to the rocket axis, the typical mounting orientation for mass spectrometers. More than 800 of these rockets were flown by the U.S. military and NASA between 1947 and 1985 (when the last Aerobee 150 was launched by NASA). It was a very successful vehicle that provided a soft ride for instrumentation.

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The initial instruments adapted to space flight were Bennett radio frequency mass spectrometers to study the composition and number density of the lower ionosphere [31.1.2]. They were flown on Aerobee rockets at the White Sands Missile Range, NM. The Bennett tube mass spectrometers, as they were called, consisted of cylindrical open ended tubes, mounted to look radially outward from the cylindrical rocket section. They did not contain an ion source, but instead a plane grid was mounted on the tube end flush with the rocket's surface that served as a draw in grid to extract ions from the surrounding atmosphere. These instruments were termed ion mass spectrometers (IMS) Mass separation was accomplished by passing ions resonant with the RF field and rejecting others. The sensitivity of this instrument was very high due to the large cross section of the tube, but its mass resolution was just adequate to separate the ionospheric ions. The goal was to study the composition and number density of the ionosphere. The molecular ion species, NO+ and OZ+, dominated the lower ionosphere. At higher altitudes, O+ and H+ were observed. Details of the Bennett mass spectrometer are given in Chapter 31.8.1. Subsequent development of mass spectrometers for space research lead to the miniaturization of laboratory magnetic sector field instruments. [31.1.3] Laboratory versions of these instruments typically had radii of curvature of the ion path in the magnetic field from 6 to 12 inches, while the flight instruments utilized radii in the range of 1'/2 to 2'/z inches. Miniaturized electronics control units consisted of a low-voltage power supply, several high-voltage power supplies, and logarithmic electrometer amplifiers to read the output currents from the instruments. Magnetic sector-field mass analyzers incorporated an ion source that was recessed in the side of the rocket but exposed directly to the ambient atmosphere after reaching approximately 100 km altitude. This configuration came to be known as an open source instrument. The only connection between the ion source and analyzer region was through the narrow slit defining the ion beam. The analyzer vacuum was maintained at a lower pressure than the ion source with a sputter ion pump making operation possible at higher source pressures (lower altitude). Also back-streaming from analyzer to source was minimized as the rocket rotates causing the source pressure to vary by a factor of 1000 in less than 2 sec. allowing the ram and wake gas pressure to be followed. The first flight of the neutral gas mass spectrometer occurred on June 6, 1963 at White Sands Missile Range on an Aerobee rocket. [31.1.4]. Two magnetic mass spectrometers were employed. One, a double-focusing instrument, included an electrostatic analyzer in tandem with the magnetic analyzer. The 4 of 130



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other was a 90° single-focusing magnetic instrument. The two spectrometers were mounted 180° apart in the cylindrical section of the rocket. The rocket reached an altitude of 209 km; the caps covering the ion sources were ejected at 104 km. Since the ion sources were looking outward radially to the rocket axis, the rolling of the rocket produced a continuously changing angle of attack yielding a distinct roll modulation to the data. Results showing the roll modulated spectra for N Z and atomic oxygen were obtained as were the total particle density as a function of altitude are shown in Figure 31.1.1. Argon and neon peaks show that diffusive separation begins to occur below 100 km rather than above as was generally assumed [31.1.5].

N2 PEAK vs ALTITUDE

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ALTITUDE (km)

Figure 31.1.1 Roll modulation of the N2 peak due to continuing change in rocket attitude. Details of the magnetic mass spectrometers are given in Section 31.9. Magnetic sector field mass spectrometers were also developed for ionospheric composition studies. The ion source was replaced with a screen mounted flush with the surface of the rocket. The screen was maintained at a negative voltage of typically -6 volts to draw in positive ions from the ionosphere. The object slit of the mass analyzer had to be set at rocket/satellite ground potential mass analyzer. Rather than at the usual sweep high voltage as in a neutral gas instrument since ambient ions have only a few volts of energy due to the rocket motion. The mass analyzer was insulated from the rocket ground potential and was swept from a negative high voltage towards ground potential in order to scan the mass spectrum. The ion detector was an electron multiplier whose input end was at a high negative voltage. The output from the electron multiplier was at rocket ground potential. A logarithmic electrometer amplifier detected the current. Due to the electron multiplier gain, the sensitivity of this instrument was 5of130



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very high and rivaled that of the Bennett rf spectrometer which achieved its sensitivity due to its wide open geometry. The mass resolution of the magnetic instrument was much higher than that of the Bennett rf instrument. In addition to recording the analyzed ion current, a probe intercepting a fraction of the ion beam leaving the ion source, monitored the total ion current. Absolute ion density measurements require in-flight calibration of an ion mass spectrometer. One such calibration experiment was done in 1966. [31.1.6] The Explorer 31 satellite was launched via a ThorAgena rocket along with the Canadian Alouette II satellite that contained a Top-Side sounder that measured electron density vertical profiles in the satellite vicinity while the magnetic IMS on Explorer 31 measured the ion species concentrations. Comparison of the total ion currents with the sounder electron density measurements enabled absolute number densities of ionospheric species to be obtained. Explorer XXXI orbit parameters were perigee 500 km and apogee 3000 km at an inclination of 80 degrees. In order to obtain simultaneously both horizontal and vertical profiles of ion composition an Argo D-4 (Javelin) rocket flight occurred in the daytime in 1966 timed with an over pass of the Explorer 31 satellite. Both vehicles carried identical magnetic IMSs. The rocket, launched from Wallops Island, VA, reached an altitude of 720 km while the satellite passed over at 970 km. [31.1.7] Extrapolation of the vertical profile of the rocket instrument's total ion density to the satellite altitude provided a calibration comparison with the satellite ion density data. Figure 31.1.2 shows the comparison data from both flights. PM

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The orientation of the Explorer 31 satellite in flight was such that its axis of rotation was maintained normal to its orbital plane. It rolled like a wheel along its orbit. The IMS's entrance aperture looking out from the equator of the satellite then lay in the orbit plane so it alternately pointed in the ram and wake directions. This produced a roll modulation in the data. From the offset of the maximum of the H+ ion current with respect to the ram direction, the outward flow of hydrogen ions was discovered. This flow is known as the polar wind, a flow of ions out to the magnetosphere from the ionosphere. Figure 31.1.3 is a diagram of the roll modulated data.

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Figure 31.1.3 — Ion concentration (No./CC) versus time (sec.) showing phase difference in the roll modulation maxima of H+ and 0+. The ISIS-II satellite, a joint US-Canadian project was launched in 1971 into a polar constant altitude (1400 km) orbit. It contained a set of instruments including the magnetic IMS that characterized many properties of the topside ionosphere over a period of more than 8 years. [31.1.8] The polar wind upward flow velocity is determined from the shift in the maximum angle between the H + and O+ ions profiles. A description of the magnetic IMS and the techniques used to calibrate the instrument in flight to obtain absolute ion species concentrations are given in Section 31.9. On another flight of an Argo D-4 rocket, the nighttime ionospheric composition was investigated. [31.1.9] The Lower ionosphere regions, known as the D and E layers, disappear after sunset due to recombination of the molecular ion species, NO and 0 2. Hydrogen ions become the dominant species above 420 km. The last three Apollo flights to the moon carried magnetic sector-field mass spectrometers to detect the presence of an atmosphere and determine its composition. On the Apollo 15 and 16 flights the 7 of 130



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instrument [31.1.10] was mounted in the Scientific Instrument Module of the Apollo Command and Service Module (CSM). This section of the Apollo spacecraft remained in orbit while the descent module landed on the surface. The instrument, a sector-field dual-collector mass spectrometer was mounted on a boom stowed in the SIM bay of the Apollo Service Module which was capable of extending the instrument to a distance of 7.3 meters from the spacecraft. Figure 31.1.4 is a drawing of the configuration. The purpose of the boom mount was to remove the instrument a reasonable distance from the spacecraft that would place it beyond the interacting cloud of outgassing molecules from the spacecraft, and in a collisionless, outwardly free streaming region. The instrument package was a rectangular box, 30 x 32 x 23 cm, weighing 11 kg, bisected by a base plate, with the electronics portion on one side and the mass analyzer on the other. A plenum, in the form of a scoop, was mounted on the outboard side of the package and oriented in the direction of motion. M455 SPECTRO

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Fig. 31.1.4 — Lunar Command Service Module The instrument and the boom extension and retraction was operated by an astronaut in the CSM. Measurements of the lunar atmosphere from orbit suffered from the very low density of the atmosphere and the fact that the gases had their origin from the CSM. They were captured in similar orbits around the moon. However, trace amounts of native neon were detected in the lunar atmosphere. See Section 31.11 for details of the instrumentation. The Apollo 17 mass spectrometer was deployed on the lunar surface as one of the instruments comprising the Apollo Lunar Surface Experiments Package (ALSEP). Figure 31.1.4 is a picture of the instrument sitting on the lunar surface taken by the astronaut [13.1.11]. It operated for nearly one year before a high voltage module corona disabled the instrument. 8of130



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Picture Fig. 31.1.4 — Mass spectrometer on lunar surface. Gas molecules entering the instrument aperture at the lower right corner were ionized by an electron bombardment ion source, collimated into a beam, and sent through a magnetic analyzer to the detector system. In the normal mode of operation, the fixed mode at an electron energy of 70 eV, the sensitivity to nitrogen was 5 X 10 -5 A/torr, which was sufficient to measure concentrations of gas species in the 1 X 10 torr range. An alternate mode, the cyclic mode, provides four different electron energies (70, 27, 20, and-15 18 eV) to modify the cracking pattern of complex molecules. Identification of gases in a complex mass spectrum was greatly aided when the spectra were taken at several different electron ionization energies. Also, at low energy, doubly charged peaks were eliminated from the spectrum, thus simplifying the task of identifying parent molecules. A detailed description of the lunar instruments is given in Section 31.10. Lunar gas density of 10 5 molecules per cm3 (_10-1 1 torr, —10-9 Pa) was detected at night. Argon froze on the night surface and was released in the early morning as the terminator approached the instrument site. Daytime operations were suspended when the temperature rose to the level that the site outgassing saturated the instrument with gas [31.1.12]. Mass spectrometers were flown on three Atmosphere Explorers (C, D, and E) for studying ion and neutral composition and reaction rates within the thermosphere as well as to provide measurements for studying the global structure and dynamics of the neutral atmosphere and ionosphere. Table 31.1.1 lists the flight parameters of the 3 AE satellites. In addition to several mass spectrometers, each spacecraft 9of130



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carried a retarding potential analyzer and several optical instruments [31.1.13]. See Section 31.11 for instrument descriptions.

Table 31.1.1 is a list of parameters for the three Atmosphere Explorer satellites. Atmospheric Explorer C D E Launch Date 1973 1975 1975 Orbital Inclination 200 680 900 Features Stable perigee Equatorial- local time Polar- rapid latitude surveys variations Altitude range 130 to 4000 km 150 to 3000 km 150 to 3000 km Ion composition studies were carried out with the magnetic sector ion mass spectrometer and the Bennett RF instrument [31.1.1, 31.1.2]. These instruments were similar to those flown on previous rocket and satellite missions. The magnetic ion mass spectrometer had an expanded mass range from 1 to 90 Da utilizing 3 ion trajectories through the magnet that allowed three mass ranges to be scanned simultaneously.

In addition, two neutral gas mass spectrometers, one an open source magnetic sector field instrument, the other a closed source instrument utilizing a hyperbolic rod quadrupole mass analyzer [ref] were flown on the AE series. The open source instrument was a magnetic sector-field instrument similar to those used in previous rocket flights [13.1.3]. Since the source was exposed directly to the ambient atmosphere, there was minimal, but not zero, interaction of the incoming gas stream (due to the motion of the satellite) with the instrument electrodes prior to ionization by the electron beam. The collisions with source electrodes introduced some uncertainty in relating ambient atmosphere densities with measured particle densities. The closed source instrument employed a small chamber having a knife edge orifice that connected to the atmosphere [13.1.4]. Gases flowing into this chamber accommodated to the temperature of the chamber walls through collisions. For chemically inert species it was then possible to relate the gas density in the chamber to the ambient density based on kinetic gas theory and knowledge of the vehicle velocity. However, reactive gases like atomic oxygen were lost, i. e., recombined into molecular oxygen or converted into other species like carbon dioxide. Hence the need for an open source mass 10 of 130



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spectrometer. The mass analyzer of the closed source instrument was a linear quadrupole type consisting of 4 parallel rods. Rf and DC voltages applied to the rods guided resonant ions (those of a chosen mass to charge ratio) down the axis of the rods to a collector. Non-resonant ions were scattered out of the beam. This type of instrument was first flown on OGO-6 and SanMarco-3 satellites. Instrument details are given in Section 31.11. In December 1978, seven gas analyzers made in situ measurements of the Venus atmosphere chemical composition. Three mass spectrometers and two gas chromatographs sampled the lower atmosphere (from 65 km to the surface) while two mass spectrometers sampled the upper atmosphere above 120 km from satellites. The lower atmosphere mass spectrometers were flown on the USA Pioneer Venus Multiprobe Sounder probe [31.1.14] and on the USSR Venera 11 and 12 landers [31.1.15]. The gas chromatographs were carried on the Pioneer Venus probe and Venera 12. One upper atmosphere mass spectrometer was on the Pioneer Venus multiprobe bus and one on the Pioneer Venus Orbiter. Several types of mass analyzers were employed in the various instruments. See Section 31. 12 for the instrument descriptions. The Pioneer Venus Sounder probe and the Pioneer Venus Bus instruments contained magnetic sector analyzers; the Pioneer Venus Orbiter analyzer was a quadrupole; the Venera instruments had Bennett Rf analyzers. In addition to the neutral gas'mass spectrometers, identical Bennett Ion mass spectrometers were incorporated in the Orbiter and Bus.

Shortly after the Sounder Probe encountered the top of the Venus atmosphere and its heat shield ejected by deployment of the parachute, the instruments were activated and data were gathered from this point, at an altitude of 62 km, to loss of signal at the surface. For the first 17 min the probe floated down on a parachute. After parachute jettison an additional 37 min elapsed before the probe reached the surface. The neutral mass spectrometer on the Sounder Probe [31.1.16] sampled the atmosphere through a pair of microleaks that protruded through the side of the Sounder Probe's aeroshell, beyond the probe's boundary layer, into the freestreaming atmospheric gases. In this way sampling of the atmosphere was free from contamination by vapors emitted from the probe's surface. The two leak's conductance differed by a factor of 10, the larger one being used in the upper more rarified atmosphere. From approximately 50 to 28 km the leaks were blocked by an overcoating of cloud particle materials, presumably by droplets of sulfuric acid cloud particles. During this time the in-flow of atmospheric gases was stopped and mainly background or residual gases in the mass spectrometer were seen, except for SOS and H2O which appeared to originate from the blocking material. Below 30 km the primary 11 of 130



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leak reopened (the secondary leak had been valved off by this time), and the atmospheric gas flow returned to normal. A fortuitous result of the blockage was the opportunity to measure the isotopic composition of the Venus water since the overcoating material was water that condensed from the clouds. The water peaks were very large enabling the oxygen and deuterium/hydrogen ratios to be measured knowing that the water was indeed from Venus. The D/H ratio was 0.016, a hundredfold increase over earth's D/H ratio [13.1.17]. This result means that at least 0.3 percent of a terrestrial ocean was outgassed from Venus, but is consistent with a much greater production. Data from each of these instruments showed reasonable agreement between the abundances for different gas species, generally to better than a factor of 2 [31.1.18]. One of the principle discoveries was the excess, relative to earth, of the primordial isotopes of the noble gasses, neon and argon by a factor of over 200 [ref]. However, the radiogenic isotope of argon, 40 A abundance is similar to that on earth. There is also a significance abundance of sulfur compounds below 22 km. Bennett radio frequency ion mass spectrometer instruments on the Pioneer Venus Bus (BIMS) and Orbiter (OlMS) are identical both electrically and mechanically. [31.12.4]The sensitivity, resolution, and dynamic range are sufficient to provide measurements of the solar-wind-induced bow-shock, the ionopause, and highly structured distributions of up to 16 thermal ion species within the ionosphere. The use of adaptive scan and detection circuits and servo-controlled logic for ion mass and energy analysis permits detection of ion concentrations as low as 5 ions/cm3 and ion flow velocities as large as 9 km/s for O +. A variety of commandable modes provides ion sampling rates ranging from 0.1 to 1.6 s between measurements of a single constituent.

The Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) was designed to measure the vertical and horizontal density variations of the major neutral constituents in the upper atmosphere of Venus between the altitudes of 150 to 300 km. [31.1.19] A quadrupole mass spectrometer equipped with an electron impact ion source was the sensor employed for the composition measurements.

Each instrument is described in Section 31.12 The neutral mass spectrometer experiment (NMS) carried by the European Space Agency's Giotto spacecraft determined the abundances and the chemical, elemental and isotopic composition of the gases 12 of 130



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and low-energy ions in the coma of comet Halley [31.1.20]. The NMS consisted of two analyzers: a double focusing mass spectrometer (M analyzer) and an electrostatic energy analyzer (E analyzer). A unique situation occurred with Halley's Comet. It travels around the sun in a retrograde direction while the Giotto probe having been launched from earth travels in a prograde direction. The relative velocity between the two when passing was 69 km/sec, which equated to 25 eV per Da. Therefore, a water vapor molecule (18 Da) had a kinetic energy relative to the mass analyzer of 450 eV. Consequently an electrostatic analyzer, which is an energy analyzer, became a mass analyzer also. The mass range of the two analyzers was 8 to 86 Da for neutral gas and 1 to 56 Da for ions. The probe passed into a thick sheet of dust particles at 1000km from the comet that caused cessation of the telemetry signal. The signal was recovered after passing the comet nucleus, but most of the instruments and the camera did not survive.

A synopsis of the results showed a predominance of water vapor (80% by volume) in the coma with an H2O density of 4.7 x 107 molecules cm-3 at 1,000 km, a neutral gas expansion velocity of 0.9 km s -1 at 1,000 km and a total gas production rate of 6.9 x 10 29 molecules/cm3. The Cassini mission to Saturn launched in October 1997 arrived at Saturn in June 2004 after gravity assist boosts from Venus (twice), Earth and Jupiter. It carried the Huygens Probe that was released to enter the Titan atmosphere in January 2005 [31.1.21]. It settled through the atmosphere to the surface where it continued to operate for 90 minutes. The probe carried 6 instruments, one being a gas chromatograph-mass spectrometer (GC/MS) that was designed to identify and measure chemicals in Titan's atmosphere. It was equipped with samplers that were filled at high altitude for analysis by the mass spectrometer, a high-voltage quadrupole. During descent, the GUMS also analyzed aerosols collected by filters and pyrolyzed (i.e., altered by heating). Finally, the GUMS measured the composition of Titan's surface by heating the GUMS instrument just prior to impact in order to vaporize the surface material upon contact.

The Huygens probe measured the surface temperature to be —179°C [31.1.22]. Titan rains are mainly methane and ethane. Although Huygens saw no seas of such exotic liquids, lakes of this concoction have now been confirmed at high latitudes. Huygens itself landed in a riverbed, which, although dry at the time of the landing, probably funnels the methane rain off the hills and onto the lower ground. Dark organic compounds containing amino and nitrile groups created in the upper atmosphere also drift down 13 of 130



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to coat the moon's surface and mix with ice grains to form sand-like material which settles in longitudinal dunes. Besides methane, there is an abundant amount of nitrogen in the Titan atmosphere but with an isotopic ratio somewhat depleted of 14N indicating that roughly 5 times the present amount of atmosphere has escaped over time. Carbon, which is present in methane does not show such depletion of 12C. This result indicates that methane is continuously being replaced in the Titan atmosphere possibly by cryovolcanism. The discovery of 40Ar in the atmosphere indicated that rock formations exist below the icy mantle and this could be the source of the volcanic emissions into the atmosphere. The composition of the Mars atmosphere has been explored by three spacecraft whose payload contained a mass spectrometer. In 1976, Viking 1 and 2 landed on Mars at sites 22'N and 45'N respectively [31.1.23]. In each spacecraft there were two double focusing magnetic mass spectrometers, one to sample the atmosphere during the descent to the surface; the other to measure the gases in the atmosphere at the surface and to serve as the gas analyzer for effluents evolved from surface sample heated in a small oven. An arm and scoop dug soil samples from the surface and deposited them in each of 3 containers, one of which was fitted with a heating coil to raise its temperature to 500 °C. The analysis was done with a gas chromatograph coupled to the mass spectrometer. One of the goals was to search for hydrocarbons. However, none were found. Atmosphere data showed the presence of nitrogen and argon at the few percent level in the dominant CO2 atmosphere [31.1.24]. The Phoenix spacecraft that was launched to Mars in August 2007 landed safely on the Martian northern arctic region on May 25, 2008 [31.1.25]. It carried 6 experiments to study the history of water on the planet and search for organic molecules in the icy subsurface Martian soil. Data from the Mars Odyssey Orbiter spacecraft neutron monitor showed large amounts of subsurface water-ice in the northern arctic plains. The spacecraft was a lander with an arm and scoop designed to dig a trench though the top soil to reach an expected ice layer near the surface. One of the instruments, the Thermal Evolved Gas Analyzer, TEGA, consisted of two components, a set of 8 very small ovens that heated samples of the ice-soil mixtures from the trenches to 1000 °C to release imbedded gases and mineral decomposition products, and a mass spectrometer that served as the analysis tool for the evolved gases and also for measurements of the composition and isotopic ratios of the gases that comprise the atmosphere of Mars. The mass spectrometer was a miniature magnetic sector instrument controlled by microprocessor driven power supplies. The lander operated for 5 months until, as the season changed from summer to fall, the 14 of 130



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solar energy input decreased and temperatures fell, the lander stopped operating. A hard, icy-soil mixture was found 5 cm below the surface covered with a rather fine layer of soil-regolith material. The icy soil mixture was heated in one of the ovens. The presence of water was confirmed in the sample. This was a major goal of the mission. Calcium carbonate and magnesium perchlorate (completely unexpected) were found in the soil samples [31.1.26]. Again, no hydrocarbons were observed. Section 31.13 contains a detailed discussion of the experimental techniques, instrumentation and results.

31.1.2 Mass Spectrometers in the Manned Space Programs — Medical Applications

The manned space program has used mass spectrometry for environmental monitoring and as a tool in medical experiments. Although the environmental monitoring applications of mass spectrometry (next section) now dominate spacecraft operations, it was the medical use of mass spectrometry that first occurred aboard a crewed spacecraft. Skylab was the first "orbital" laboratory with the goal of studying the effects of microgravity on astronaut's health and performance [31.1.2.1]. Consequently, the medically astute crew participated in numerous medical experiments. The first mass spectrometer was designed to assess the impact of micro-gravity on the body's physiological response to exercise. Toward this end the mass spectrometer, in experiment M171, named the Metabolic Study Gas Analyzer System (MGAS) measured gases in the expired breath [31.1.2.2]. Data from the Apollo program had shown that most astronauts demonstrated a reduced tolerance for exercise during a period of hours after landing. Was this condition exacerbated as mission length increased? This was a question that had to be studied and addressed before astronauts conducted long duration (months) missions [31.1.2.3].

Measurement of metabolic performance in the laboratory was a complex, multi-step task that required highly-trained physiological technicians to derive accurate results. [31.1.2.4] The MGAS design was driven by the need to convert the complex laboratory metabolic performance measurements into a mostly automated task that could be performed on orbit by crewmembers. The metabolic analyzer had to measure oxygen, nitrogen, carbon dioxide, and water vapor over a wide range of concentrations that was depended on exercise protocol and environmental conditions. Mass spectrometry was considered the best technology for the analyzer, although its complexity was recognized as a difficult design issue for keeping the unit small. [31.1.2.5] At this time NASA was having Perkin-Elmer develop a prototype 15 of 130



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mass spectrometer for air analysis in spacecraft and it seemed that only a few modifications were needed for it to function as the metabolic gas analyzer. The MGAS analyzer was a single focusing magnetic sector mass spectrometer with a mass range of 2-50 amu, which was sufficient to span the molecular weight range of the target gases . ( Figure 31.1.2.1). [31.1.2.6] The WE 28 COtIFCTa 2 COLLECTOR VE

44

metabolic pulmonary function was derived from these and other

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measurements. The results from this experiment and others on COL` ECIOR

Skylab demonstrated man's ability to adapt to the microgravity

Figure 31 . 1.2.1 — Typical mass peaks environment and to quickly re-adapt to Earth's gravity. In this and collector alignment experiment there was a direct correlation between the crew's extensive exercise on orbit and their short recovery time when returned to Earth; therefore length of stay on orbit need not be a factor in readaption time.

An improved version of the MGAS, called the Gas Analyzer Mass Spectrometer (GAMS) was built for use on Shuttle's biomedical laboratory missions that flew between 1989 and 1995. The GAMS increased the mass range ( 2-120 amu) and the number of compounds measured to nine (nitrogen, oxygen, carbon dioxide, water vapor, isotopic carbon monoxide, nitrous oxide, argon, helium, acetylene, and total hydrocarbons ( m/e 50 -120). [31.1.2.7]

The newest version of the metabolic gas analyzer used on ISS is the Gas Analyzer Metabolic and Physiology ( GASMAP), which is a quadrupole mass spectrometer • •

` ^'-' t with significantly improved capabilities when compared to the GAMS.

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The GASMAP was manufactured by Marquette Electronics Industries (MEI). The GASMAP (Figure 31.1.2.2) extended the mass range to include sulfur hexafluoride ( SF6) and it has improved scanning capabilities over the GAMS device. The GASMAP has been used for

Figure 31.1.2.2 — GASMAP

a number of in-flight physiological experiments, most involving the

use of S176 to track respiration capability. [ 31.1.2.8]

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31.1.3 Mass Spectrometers in the Manned Space Programs — Environmental Monitoring Applications

NASA was concerned from the very beginning of the space program about the impact of materials offgassing on crew health. As early as 1963, the Apollo design teams recognized the unique challenge of contamination from materials offgassing in the Apollo command module. For the first time crews in the Apollo command module would be continuously exposed to recycled air in a closed-environmental system. [31.1.2.9] Consequently, a rigorous materials screening program was implemented, which included offgas testing [31.1.2.10] whereby a material's propensity for releasing toxic contaminants was assessed. In 1968, the National Academy of Sciences (NAS) panel on Air Standards identified 200 potential contaminants that might be found in spacecraft air. [31.1.2.11 ] Another NAS panel established emergency exposure limits for a number of toxic compounds that could accumulate in the spacecraft. The emergency exposure limits were based upon a one-time exposure and permitted some level of reversible symptoms [31.1.2.12], as opposed to the MACs that were set at a no effect concentration.

In 1988, the advent of the International Space Station (ISS) program led to the decision to provide stronger documentation for the Spacecraft Maximum Allowable Concentrations (SMACs). It is impossible to set rigorous limits for hundreds of potential contaminants, so the list was culled to a manageable size. vitorraonwuswx+

Compounds requiring SMACs were either those that had

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previous archival samples, compounds frequently detected in offgas testing, and/or compounds that were harmful to humans (i.e., benzene) or equipment (catalytic poison) even

at low concentrations (parts per billion - ppb). These Figure 31.1.2.3 — Sources of compounds can arise from a number of sources (Figure contamination on spacecraft 31.1.2.3) aboard a spacecraft, but unknowns are rare due to the effective materials control program.

Toxicologists at JSC would propose SMACs, based upon literature reviews, to a National Research Council (NRC) expert panel on toxicology. Following NRC input and discussion, the .compound's SMAC document was approved after revisions, if required. The approved SMACs are listed in JSC documents [31.1.2.12], but the full documentation of each compound and the process for establishing 17 of 130



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SMACS are published by the NRC. [31.1.2.13-19] The SMAC for a compound is not a single value but a range (I-hr, 24-hr, 7-day, 30-day, and 180-day), which covers different length missions and emergency scenarios. Like the previously mentioned emergency exposure limits, only the 1-hr and 24hr SMACs allowed temporary, minor/mild crew symptoms to occur.

The purpose of the ground-based analysis of archival samples and the more recent real-time monitoring of spacecraft contaminants is to assess the air quality during crewed missions (acceptable or established limits were exceeded). Furthermore, the SMACs are used in the calculations of the offgas testing to identify items that could release contaminants at unacceptable concentrations. These tests are a required part of theflight hardware certification for materials, assembled items, and modules.

31.1.3.1

Groundbased GC/MS Analysis of Samples

Early manned spaceflight vehicles (Mercury, Gemini, and Apollo) were too small to accommodate instrumentation for atmospheric composition or air quality measurements, other than electrochemical r' sensors for critical gases such as oxygen. Consequently, the initial application of mass spectrometry for manned missions occurred in ground-based laboratories. Characterizing the types of pollutants released into spacecraft during a mission was first achieved through analyses of the contaminants collected on the spacecraft air scrubbers. [31.1.2.20-21] The improvements to GC/MS in the late 50s and early 60s was quickly establishing it as an excellent method for analyzing complex mixtures of VOCs; therefore it was only logical for NASA to adopt GC/MS for analysis of spacecraft air contaminants. [31.1.2.22] An important advantage of GC/MS analysis for NASA was the instrument's ability to accurately identify compounds in a mixture, since the contaminants released into spacecraft air were not known. The charcoal analyses weren't quantitative, but they did provide valuable information on contaminants in a spacecraft environment. Within the limits of the technique, the analyses of Apollo samples showed acceptable cabin air quality, which meant the materials control program and the Environmental Control and Life Support (ECLS) system were effective in controlling pollutants. [31.1.2.23]

Skylab was the first U.S. spacecraft in which direct samples of the spacecraft atmosphere were acquired and returned to the ground for analysis. Skylab (1972-1974) signaled a change in spacecraft from mainly a means of transportation to a habitation facility and workplace [31.1.50]. The Skylab program 18 of 130



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saw the development of the first archival air samplers specifically designed to trap the VOCs in the air rather than rely upon the analysis of accumulated VOCs in the scrubber's charcoal [31.1.51 ]. The samples were returned to the ground and analyzed by GUMS. Of the 300 compounds detected, 107 were identified with molecular weights ranging from 60-584 amu.

The Shuttle was a relatively small vehicle that could house up to seven people for 30 days and the worries about increasing trace contaminant levels in such a "crowded" vehicle led to a rigorous archival air sampling strategy. The Shuttle's main sampling device is a grab sample container (GSC) shown in figure 31.1.2.4 , but a Solid Sorbent Air Sampler (SSAS) was also flown on the first mission of a new or refurbished Shuttle. The SSAS was designed (Figure 31.1.2.5a and b) to acquire seven, 24-hour samples during a mission. The Solid Sorbent Air Sampler (SSAS) contained eight glass-lined stainless steel Tenax-filled tubes that were connected to a 16-port, 8-position stainless steel Valco rotary valve [31.1.2.26-27].

ir Ca so

Figure 31.1.2.4 GSC

Figure 31.1.2.5a — Solid Sorbent Air Sampler Figure 31.1.2.5b — SSAS on orbit

This valve isolated the tube, once the sample was acquired, thus preventing cross-contamination of the sample. In addition to the aforementioned Shuttle flights, the SSAS was used on the medical sciences laboratory and longer duration Shuttle flights from 1985-2003 and also on MIR and ISS during this time period.

The GSC is a standard 300 ml Summa TM-treated canister that is similar, albeit smaller, than the canisters used by the Environmental Protection Agency (EPA) for collection of trace volatile organic compounds (31.1.2.28). These samplers provided data on VOCs as well as other more volatile spacecraft air

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Ch 31 MS in Space

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contaminants, such as carbon monoxide and carbon dioxide, that aren't trapped by the sorbent tube samplers (SSAS).

A GSC sample (pre-flight) is acquired in the crew cabin before launch and a flight GSC is used to sample the cabin on the last day of flight. A third GSC is reserved for contingency situation (odor, smoke, etc.) during the mission. Upon return of the samples to the Toxicology Laboratory at JSC, several GC runs are performed to analyze for the lighter gases (CO, CO 2 , CH4, and H2) and the hydrocarbon loading.

The bulk of the trace contaminant analysis from the GSCs is performed on a gas chromatograph/mass spectrometry (GC/MS) system (Figure 31.1.2.10). The Toxicology laboratory has adopted modified versions of TO-14/TO-15 (GSC analysis) and TO-1 /TO-17 (sorbent tube analysis) methods. [31.1.2.29] Modifications are needed to address the constraints of spaceflight, such as limited availability of duplicate samples and trip controls. Nominally, a 100 cc sample is obtained from the GSC by an Entech7100 Preconcentrator system, which concentrates the VOC while removing water and CO, in a series of traps. The Figure 31.1.2.10 — An operator final desorption from the Entech sends the sample plug of performing AIS/GC/ MS analysis in in an Agilent 6890N GC. The GC is connected to an Agilent 5975 VOCs to a GC column (150 quadrupole mass spectrometer.

In addition to Shuttle, the GSCs are also part of a larger suite of analytical tools for assessing the quality of the atmosphere on ISS. Three GSC samples are acquired each month with one sample rotated among the various modules and the other two samplers always used for the U.S. Laboratory (LAB) and Russian Service (SM) modules. The samples are returned to Earth via the Shuttle approximately every three months (total of 12 samplers per mission). The analyses on these samplers are conducted as presented for the Shuttle GSCs

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A NASA grant had propelled Pete Palmer, a researcher at San Diego State University, to conduct an investigation of mass spectrometry techniques for analyzing air contaminants. Dr. Palmer assessed GC/MS, TD(thermal desorption)/GC/MS, and MS/MS as possible means to achieve analysis of a wide. variety of contaminants in spacecraft air. [31.1.2.30] Later, Dr. Palmer analyzed several samples returned from the MIR spacecraft by Direct Sampling Ion Trap Mass Spectrometry (DSITMS), which has the advantage of very fast analysis by a much less complex instrument (no GCs and associated gases). The analyses of the MIR samples showed the potential of DSITMS to detect the pollutants at levels well-below the SMACs and to analyze a broad range of compounds. [31.1.2.31 ] Ultimately, ground analysis continued with GC/MS because the EPA had developed their methods around this technique and it provided a documented and verifiable analysis.

31.1.3.2

Inflight Use of Mass Spectrometry

Interestingly at the time Perkin-Elmer was developing the MGAS, the U.S. Navy was looking for a submarine atmospheric monitoring system, because the system being used at the time was unreliable. The U.S. Navy saw potential for the MGAS to meet their needs with minimal modifications. Trial results convinced the Navy to have Perkin-Elmer build a similar system for submarine atmospheric monitoring. [31.1.2.32] The first version built was the Central Atmosphere Monitoring System Mark I (CAMS)-I, which performed as expected, but has since been replaced by an improved version, the CAMS-II. [31.1.2.33]

The pedigree for the International Space Station's Major Constituent Analyzer (MCA)-is from the MGAS and the U.S. Navy's CAMS and as such it is a single-focusing magnetic sector mass spectrometer. Designed to monitor the major constituents (oxygen, nitrogen, hydrogen, carbon dioxide, methane, and water vapor), it became the first mass spectrometer used for routine environmental monitoring on a manned spacecraft. [31.1.2.34] The data from the MCA is used to meet two necessary ISS requirements: 1) feedback for environmental control and life support (ECLS) systems and 2) verification that oxygen concentration meet medical requirements and that carbon dioxide and methane concentrations are below toxicological limits (SMACs).

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The MCA (Figure 31.1.11), built by Perkin-Elmer (later Orbital Sciences), was comprised of seven onorbit replaceable units (ORUs). [31.1.2.35] The ORUs (detailed description in section 31.2.7) have been essential to maintaining operation of this critical piece of equipment. The MCA has a calibration gas that is used to check and adjust the MCA's calibration once per week. MCA provides the feedback information to control the oxygen concentration in all situations onboard ISS. During Extravehicular Activities (EVAs), the oxygen concentration in parts of the ISS is adjusted for this lower pressure activity and tight control of the oxygen levels is important not only for crew health, but also for resource management. The MCA accuracy requirements are shown in Table 31.1.2.1. As will be discussed in section 31.7, the water accuracies for water and carbon dioxide were changed to "non-specified" and ±3%. Other activities, such as docking spacecraft or a failure of a primary oxygen generation system (Russian Elektron and U.S. OGS) can alter the ISS oxygen concentration. If the addition of oxygen is Table 31.1.2.1: MCA Range and Accuracy requirements Monitored Range Accuracy (Torr) (%FS) Gas Nitrogen 335 —800 f2 0-300 ± 2 Oxygen 0-50 ± 5 Hydrogen 0-25 ± 5 Methane 0-25 ± 5 Water Carbon 015 ±1 Dioxide Figure3l .l .2.11 — Major Constituent Analyzer then reserve oxygen can be depleted quickly in the large ISS volume. Additionally, the MCA's measurements provide a means to monitor the performance of the carbon dioxide scrubbing systems (Carbon Dioxide Removal System-CDRA and Vozduk-Russian CO 2 removal system) and to verify that CO2 levels are maintained below the established SMACs.

31.1.3.3

Complementary Techniques

The International Space Station (ISS) presented a different operational scenario with its envisioned large habitable volume and planned lengthy stays on orbit for crewmembers that demanded real-time air quality monitoring. The frequency (-4 times per year) of spacecraft visits to ISS meant that gaps in 22 of 130



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assessing the air quality could easily stretch to 3 - 6 months before archival samplers were returned and analyzed. Consequently, the Crew Health Care System (CheCS) and the ECLS groups had documented requirements to monitor trace contaminants in ISS for crew health and system performance evaluation, respectively.

The Toxicology group was charged with defining the requirements and identifying potential technologies for air quality monitoring aboard ISS, which included trace contaminant monitoring. In the late 1980s, the primary effort of the Toxicology group was directed toward a gas chromatograph/ion trap detector system, which seemed to be a system that could be "shrunk" to a size accommodated by ISS. In the early 1990s, three converging events completely changed the Toxicology Laboratory's direction away from mass spectrometry and toward ion mobility spectrometry (IMS). The first was the recognition by the NASA toxicologist that it was unnecessary, from a crew health perspective, to monitor 200 compounds. In fact, a list of 25-30 compounds seemed sufficient to address both crew health and ECLS needs. The 2 nd event was the recognition that ion mobility spectrometry (IMS) might be useful in the detection of VOCs in spacecraft atmosphere. Several successful flights to monitor hydrazine by IMS (Figure 31.1.2.12),

Figure 31.1.2.12 —Hydrazine monitor being used in the airlock following an EVA

using a modified Chemical Agent Monitor (CAM) from Graseby Dynamics, demonstrated the appropriateness of the technology for spaceflight. [31.1.2.36]

It seemed that IMS could be a viable candidate for trace contaminant monitoring, if a GC column could be mated with the detector. [31.1.2.37] The final event was the reduction in allocated power for equipment on ISS. The ISS program realized there was a significant deficit between the power requested by users and the projected ISS power that would be available. In 1992, the Toxicology Laboratory funded the manufacture of a breadboard volatile organic analyzer (VOA) to show the potential of IMS to meet the trace contaminant monitoring requirements. The breadboard was demonstrated for McDonnell-Douglas, the prime contractor for the ISS CHeCS program and they were impressed with its performance and small size. 23 of 130


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Figure 31.1.2.13 — TCM's mass spectrometer

The ISS program reasoned that one instrument could meet ECLS and CHeCS requirements and that they could only afford (cost and resource) one trace contaminant monitor. Breadboards of both technologies (GC/MS and GC/IMS) had been built and they generated modest amounts of data, but neither produced definitive evidence of superior performance. After several years of meetings, data presentations, and significant work by both teams, the decision to select the VOA was ultimately based upon monetary considerations: the VOA was far cheaper than the TCM.

The flight VOA, built by Graseby Dynamics (now SmithsDetection), was comprised of redundant preconcentrators (carboxen and carbotrap), 60-meter GC columns, and identical ion mobility spectrometers. [31.1.2.39] All of this was squeezed into a 0.042 in (1.5 ft) package that weighed approximately 50 kg (I 10 lbs). The GC carrier gas was nitrogen plumbed from the ISS nitrogen reserve. The two-channel VOA provided a system that could lose one channel and still provide approximately 90% of its performance. The VOA was calibrated for its target compounds (Table 31.1.2.2 ) prior to launch.

The VOA (Figure 31.1.2.14), using GC/IMS technology, was launched to ISS in August 2001.

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Compound Name Methanol 1-butanol Ethanal m,p xylenes o xylene Toluene Dichloromethane Propanone 2-butanone ethyl acetate

Compound Name Ethanol 2-methyl 2-propanol Benzene (F22) chlorodifluoromethane 1,1,1, trichloroethane (F113) 1,1,2-trichloro-1,2,2trifluoroethane Hexane Isoprene (halon 1301) trifIuorobromomethane

2-propanol

Figure 31.1.14 VOA on orbit

Table 31.1.2.2: VOA Target Compounds

The VOA encountered communications problems in the first 6 months on orbit, but the problems were solved by Spring 2002. The VOA developed a serious problem toward the end of 2003 when blown fuses disabled both channels of the instrument. [31.1.2.40] In 2005, an in-flight maintenance (IFM) replaced the blown fuses and the VOA (at least one channel) provided data from January 2006 through August 2009 when it was decommissioned. [31.1.2.41 ] The VOA suppliedkey data following the METOX incident in February 2002 [31.1.2.42] and after the Elektron (oxygen generation system) overheating in the Russian SM in September 2006. [31.1.2.43] These are discussed in greater detail in section 317. Although these were the high profile incidents, it should be noted that the VOA produced data on air quality during the early critical period after the Columbia accident (2003), when it was nearly impossible to get GSC samples returned.

Representative VOA data and its comparison to GSC analysis for ethanol and n-butanol during 2007 are shown in Figures 31.1.2.15a and 31.1.2.15b. Some compounds, such as ethanol, have fluctuating concentrations and others, such as n-butanol, have low, relatively stable concentrations in the spacecraft.

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The VOA, as a field-portable trace VOCs instrument, was a powerful analytical tool for its time; but the march of technology and the transition of NASA's mission to Exploration pointed to the need for a next generation device. The VOA was very reliable, with no component (except the fuses added very late in the design) failing until 3 years after its design life (5 years). Furthermore, with only minor adjustments to calibration curves, the VOA quantification capability continued to meet requirements (see section 31.7. for its entire 8 years on orbit without recalibration. On the negative side, the VOA was large and complex, which precluded easy on orbit repair or replacement. Reliance on ISS resources (nitrogen, rack cooling, data, and power) limited the use of the VOA at crucial times, such as when the Shuttle was docked. Finally, the VOA was a custom instrument, which meant this was the "beta" version and it was expensive to build and maintain.

It was with the aforementioned drivers in mind that the Toxicology Laboratory began investigating a new technology in the mid 2000s called differential mobility spectrometry (DMS). [31.1.2.44] This detector technology was derived from ion mobility spectrometry, but a great reduction in size and an increase in sensitivity could be realized with DMS technology. Furthermore, DMS appeared to achieve greater resolution for lower molecular weight molecules, which included most of the compounds in Toxicology's target list. Sionex introduced the microAnalyzer TM , a smaller version of the previous GC/DMS system. [31.1.2.45] This system was 1/1 O th the size and weight of the VOA and it was recognized as a leap forward in the technology of field-deployable VOCs analyzers. One advantage of this system is that air is used as the carrier gas, so pressurized cylinders of carrier gas are not required. 26 of 130



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This not only eliminates a consumable and a large gas cylinder, but it drastically shrinks the instrument, because of simplified valving and pneumatic flows. In 2008, two of these units were certified and calibrated (triplicate at 5 concentration points) for manifesting on ISS as a Station Detailed Test Objective (SDTO) experiment. The two units arrived on ISS in February 2009 and one unit was activated in May 2009 (Figure 31.1.2.16). This SDTO is undergoing evaluation for possibility replacing the VOA function on ISS and for 8 months the unit has performed well. Representative GC chromatograms from the first 4 months on orbit are shown in Figure 31.1.2.17. . 20s^M-200 N,,, ,ft2

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Figure 31.1.2.17 — Representative GC Figure 31.1.2.16 — microAnalyzer SDTO(circled) on orbit traces from four months of microAnalyzer runs The Vehicle Cabin Air Monitor (VCAM) is scheduled to be sent as a technology demonstration to ISS in March 2010. [31.1.2.46 and 47] The VCAM has a gas chromatograph (I Om carbowax column) connected to a Paul ion trap. It has a miniaturized inlet and preconcentrator (carboxen 1000) and the vacuum is provided by a small roughing pump and turbomolecular pump. The VCAM has the onboard processing capability to analysis the data and report the findings. The carrier gas (helium) and calibrant mixture are items that must be replaced about once per year. The VCAM was designed to measure both major constituents (O Z, NZ, etc.) and a target list of trace VOCs. The VCAM will be the first evaluation of mass spectrometry used to measure trace organic contaminants in spacecraft air. An advantage of mass spectrometry is its recognized capability to identify unknowns by comparison of the unknown's spectrum to library spectra.

31.1.4 Using Mass Spectrometers for Launch Vehicle Processing

Vehicles and payloads in the aerospace industry often use mass spectrometer-based gas analysis for leak integrity testing and hazard mitigation monitoring to ensure the safe operation of launch vehicles. 27 of 130



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In general, heavy lift rockets use liquid hydrogen (LH2) and liquid oxygen (LOx) as propellants. These commodities represent several hazards, primarily due to their wide flammability range. When loading a vehicle with LH2 or LOx, it is common to purge the storage areas, transfer lines, and vent lines with either nitrogen or helium. Initially, a purge is used to remove contaminants, primarily oxygen and water. This purge is continued throughout the fueling operation and only ends when the operation is completed (such as vehicle launch). The purging process prevents contamination, vent propellant vapors controllably, and dilutes a possible leak below hazardous levels if integrity is lost. It is often important to monitor for hazardous commodities in the parts-per-million levels, well below the percent levels required for flammability. The low concentration monitoring is needed, because of the intentional dilution of the purge gas and the fact that most of the leak checks are preformed with the systems at pressures well below that utilized during operation. Therefore, it is necessary to monitor these commodities at part-per-million (ppm) levels and extrapolate the results to what leak rate is occurring at the source and while under operating pressures. These leak detections have proven invaluable and are credited with saving multiple vehicles and human lives.

A variety of systems, under the general description of Hazardous Gas Detection System (HGDS), are used to perform these leak tests. At a minimum, these systems need to quantitatively monitor hydrogen, helium, nitrogen, oxygen, and argon. Hydrogen and oxygen are monitored due to flammability hazard. Nitrogen is also monitored since it is a purge gas, which is important to determine if there is a leak between helium and nitrogen purge cavities and for occasional specialized tests. Helium is monitored both as a purge gas and as a leak test tracer gas. Argon is monitored to determine if oxygen originates from a propellant leak source or air intrusion. These ground-based systems have their own sample delivery subsystems, computer control, data acquisition, and mass spectrometers. Mass spectrometry is the best choice as the detection method for these commodities since, it is ideally suited for qualitative as well as quantitative analysis; it is robust, and it can be incorporated into a remotely operated system. Essentially no other instrument can identify and selectively quantify helium and other components simultaneously. Mass spectrometers also provide quantitative information and typically have linear dynamic ranges of 5-orders of magnitude or more. Mass spectrometers also have rapid response times, with sub-second response and recovery times being common.

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In the early 1960s, NASA began to use mass spectrometers for vehicle leak detection with the Saturn Hazardous Gas Detection System (HGDS), which was first used on Saturn I launches from Launch Complexes 34 and 37. This same type of system was then used to support the Saturn V missions beginning with Apollo 4, the first unmanned test flight on 9 November 1967. The Saturn-HGDS monitored hydrogen, helium, oxygen, and argon, consisted of a diffusion pumped residual gas analyzer, and a had a sample delivery system allowing leak integrity monitoring of the S-IC, S-II, and S-IVB engines, Instrument Unit, and interstage areas. Installed in the lower level of the Mobile Launch Platform (MLP), it was operational from the initiation of propellant (liquid hydrogen and liquid oxygen) flow until start of the cold helium purges of the S-II and S-IVB engines just prior to launch. The system was maintenance intensive, and required external services such as running water and liquid nitrogen to protect the analysis region from the diffusion pump's hot oil, but it never caused a launch countdown hold or delay of any kind. Although only minor leakage was detected during the Apollo program, the HGDS became an integral part of NASA launch operations ground support equipment.

As was the case for the Saturn vehicles, the primary role of mass spectrometer ground based systems in the Space Shuttle Program has been the detection of cryogenic leaks before they become a hazard. And like the Saturn system, these ground-based systems have their own sample delivery subsystems, computer control, data acquisition, and mass spectrometers. There are currently a number of systems being used to process and monitor the Orbiters before each launch, which have proven invaluable in helping to ensure safe launches and have been credited with saving several vehicles: STS-6 [31.1.4.1], STS-35 [31.1.4.2], STS-38 [31.1.4.3], STS-73 [31.1.4.4], STS-93 [31.1.4.5], STS-113 [31.1.4.6], STS119 [31.1.4.7] and STS-127 [31.1.4.8, 31.1.4.9].

The Space Shuttle Hazardous Gas Detection System was required for hazardous gas detection in all purged compartments. The prototype Shuttle HGDS called for incorporating a commercial mass spectrometer with a control and data acquisition subsystem into a NASA designed sample transport subsystem, and the ability to monitor and control the system in the Launch Control Center (LCC) two miles away from the HGDS. Toward this end, NASA Engineering at KSC conducted an exhaustive review of available mass spectrometry technologies, and eventually selected the UTI Q30C. The instrument arrived at KSC in December 1975, and was integrated into the complete system during 1976. The unit was extensively tested for functionality, detection limits, dynamic range, long term drift, and 29 of 130



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other typical instrumental performance characteristics [31.1.4.10]. The prototype HGDS was shipped in May 1977 to the Stennis Space Center to support the test firings of the Space Shuttle Main Engines, where it remained in use for about twelve years, supporting testing of upgraded engines. The first operational HGDS (the "Prime" HGDS system) had four continuously pumped sample transport lines, pressure and flow health check sensors, the well proven UTI Q30C/1000 mass spectrometer system, an ion pump based vacuum chamber, and three synchronized microprocessors for control and data acquisition. KSC in-house software for these microprocessors proved to be the most challenging aspect of the project as the top-level software was written in a Pascal-like language, and 10 functions were written in machine code. System installation on Mobile Launch Platform 1 (MLP-1) began in summer of 1979, and the system was ready to support initial propellant loading tests in late 1980.

The Prime HGDS [31.1.4.11] proved to be quite capable of detecting and measuring very small leaks from the Orbiter Main Propulsion System. Each Orbiter seemed to have its own characteristic total leakage rate, typically 150-300 parts per million (ppm), all well within allowable limits. Before the maiden flight of the Shuttle Challenger, a Flight Readiness Firing Test was required to ensure that all main systems operated correctly. In this test, the countdown would proceed normally to T-0, the Orbiter main engines would ignite, but the Solid Rocket Booster engines would not ignite, and the Shuttle would remain bolted to the launch pad during a twenty second firing of the main engines. During this Flight Readiness Firing test, the HGDS detected a leak exceeding the allowable leakage by more than an order of magnitude during the engine firing phase. Subsequent ambient temperature helium leak tests at engine joints did not reveal significant leakage. A second Flight Readiness Firing Test was performed on 25 January 1984 with additional sample lines into the Orbiter aft fuselage to determine the leak location. Following additional analysis the leak was identified as a deteriorated weld repair on one of the main engines. In addition, faults were revealed in a number of the vehicle shuttle main engines, and a program wide recertification ensued. The propulsion division chief for shuttle launch operations subsequently stated that "...all the money spent on the HGDS, and all that would ever be spent, was paid for in those 20 seconds when the leak was detected." [31.1.4.12] Challenger successfully launched on 4 April 1983.

Due to the successes of the HGDS in demonstrating leaks, it was decided that redundancy was required. After a detailed engineering analysis, followed by laboratory testing of candidate mass spectrometers, 30 of 130



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the decision was made to use the Perkin Elmer MGA-1200 fixed sector as the basis of the Backup HGDS. A successor of the Navy's Central Atmosphere Monitoring System (CAMS) system [31.1.4.13], the MGA-1200 was an ion pumped, multiple collector, fixed magnetic sector that was becoming widely used in medical and industrial applications. The first systems were delivered in late 1985, and the first launch supported was on 29 September 1988 when the original and Backup HGDS systems successfully supported the Return-to-Flight activities following the Challenger accident.

In May 1990, a hydrogen leak was detected in the Orbiter Aft Fuselage and at the External Tank Orbiter Hydrogen Umbilical Disconnect on STS-35 [31.1.4.2]. As a precaution, tests were performed on the STS-38 vehicle as well, and leakage was also identified at the Hydrogen Umbilical Disconnect. After a series of tests of both vehicles, each with increased instrumentation, the leak was finally located, repaired, and STS-35 lifted off for a successful mission on 9 December 1990, and STS-38 on 15 November 1990. Following the STS-35 and STS-38 leak issues, it was determined that a new system had to be developed to monitor helium purged areas, something that ion pump based mass spectrometer systems cannot achieve. This new Hydrogen Umbilical Mass Spectrometer (HUMS) system was specifically designed to monitor the several hydrogen umbilical lines that load and unload fuel to the vehicle. On 7 May 1992, the prototype unit supported the Flight Readiness Firing of the new Endeavor Orbiter. Similar to the HGDS Backup, the Perkin Elmer MGA-1200 was again selected as the mass spectrometer, this time with a turbo-pump instead of an ion pump. The system was designed to monitor up to 8 sample lines, with a later modification to allow up to 21 sample lines. The computer control and operation utilized the latest technology including touch screen local operation and full remote operation. The addition of the HUMS greatly increased the capabilities of the HGDS suite of systems, making it a requirement that three mass spectrometers be utilized for the launch of each Shuttle. The HGDS utilized by NASA proved so successful that the United States Air Force incorporated a similar design for their Atlas V rocket.

In the 1997, a project began to replace the aging and unserviceable Primary and Backup HGDS units with a single system — the Hazardous Gas Detection System 2000 (HGDS 2k). The design of the system [31.1.4.14] incorporated commercially available components into an overall system specifically designed by KSC Engineering to meet redundancy requirements. The new system had to meet or exceed all of the requirements of the old systems including the need to monitor and control from the 31 of 130



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LCC. The system consisted of two fully independent mass spectrometer subsystems, including the control computers, which utilize a common sample transport subsystem. The mass spectrometer subsystem utilized a Stanford Research Systems (SRS) single quadrupole RGA 100 and a custom designed vacuum system. HGDS 2k prototype first supported launch in summer 2000, and completely replaced the Prime and Backup HGDS units by 2001.

As NASA is starting a new era in human space exploration, mass spectrometry based systems continue to help place people and payloads into space. New systems incorporating the latest in mass spectrometer technology are being designed for the next generation launch vehicles that will propel humans to the moon and beyond.

Since the United States first sent rockets toward space, mass spectrometers have helped us to better understand our world and our solar system. The United States Space Program has utilized mass spectrometers to monitor the atmosphere of not only earth but of other celestial bodies, to help ensure safe breathing air for astronauts, and to safely launch vehicles into space. Such a wide range of uses is only possible because of the flexibility, robustness, and growth potential of mass spectrometers. The enduring qualities will ensure that mass spectrometers will continue to help us explore our world, or solar system, and eventual the universe.

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31.2 Leak Integrity Testing during Spacecraft Processing

Leak integrity testing is a critical aspect of spacecraft processing. Many fluids are required to launch and operate a spacecraft and these fluids typically include hydraulics, propellants (such as hydrogen, kerosene, oxygen, hydrazine and nitrogen tetroxide), and purge gases (e.g. helium, argon and nitrogen). Normally, spacecraft operations include fluids for life support (nitrogen, oxygen, carbon dioxide), pressurization (helium, argon and nitrogen), and thermal management (ammonia, Freon). When a vehicle is processed prior to launch, various leak integrity tests are performed to ensure that systems function as intended. It is common to perform leak detection using helium as the tracer, and several monographs discuss the subject in detail [31.2.1, 31.2.2]. However, the identification of leaks using argon is rare, but an example of such an application is leak testing a Star Tracker unit. A Star Tracker system (Ball Aerospace, Boulder, CO), which is part of a vehicle's navigation system, has sensitive optics and electronics requiring pressurization with argon. The Star Tracker unit was found to be "5

leaking argon at an unacceptable rate: an estimated leak rate of 8 x 10 secs (standard cubic centimeters per second) compared to the designed maximum leak rate of 2 x 10 -6 secs (3 months compared to 10 years of operation). A mass spectrometer system was prepared as an argon leak detector to locate and resolve the leak issue.

Detection and quantitation of a leak into an uncontrolled environment is a difficult task not only to perform in application, but also to model. A very rough and simplistic model is presented here (Figure 31.2.1), where QLeak is the molar flow rate [31.2.3] and

P sys, Vsys, and

Tsy s are the pressure, volume and

temperature of the leaking system. With t as time, Equation 31.2.1 is the leak rate equation, using the ideal gas approximation. (Note that R = 8.31447

cm' • MPa)

Once the pressurized gas leaks out to the

K • mol

environment, it will displace the ambient gas near the leak position. For this model an hemispherical displacement volume (V,,,,p1, Equation 31.2.2) is used, where r is the distance between the leak source and the sample uptake probe. With this model, one can approximate the argon tracer gas concentration change, A[31.1.3.r],as given in Equations 31.2.3 — 31.2.5. (Note that time, t, in this model is intended to be

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February 2010

an _ An A(P • V)

Qtàk — dt At Vsmp[ =

(31.2.1)

RTAt

1(4 3 Ir • r 3

(31.2.2)

nRT V Leak = P

.a

Vsmpl,,

(31.2.3) n RT

A[Argon] = Vi,ak =

(31.2.4)

V Smp! VSmpl P

A[Argon] = QV k

At (I ^ 1 — ^ 3

Smpl

I

\`

QLeak r At)(

J

I\

^T) (31.2.5) J

Figure 31.2.1 — System Leak Illustration

the time of flow; in practice, it is the timescale for which the assumptions of the model remains accurate. The maximum time is when the effects of diffusion, convection, and sample probe pumping invalidate the model, which is considered to be one second in this application.)

Now that a theoretical model has been developed for the application at hand, probably the most important question in instrumental analysis must be answered, "Do the instrument's capabilities coincide with the application needs?" In this application, the leak rate was estimated to be 8 x 10-5 sccs. Assuming the sample uptake probe is 3mm from the leak source, and standard conditions for pressure and temperature (0°C, 0.1MPa, thus 1 STD•L = 4.4x10 -2 mol), the argon concentration change would

A[Argon]

_

3)

2

-5 273K = 32 scc 8x10 sccs (ls) 8.31 ccA4Pa K mol 7r(0.3cm) 3 0.1M a

scc 4.4 x 10 -2 mol

— 32 mol 103 scc

=1400ppm

mol

(31.2.6a) (31.2.6b)

be 1400 ppm, as illustrated in Equation 31.2.6. The observation of 1400 ppm is definitely within the capabilities of most mass spectrometer configurations. However, the goal is not to demonstrate that the component leaks — rather to find the leak, fix it, and then demonstrate that the component is within 34 of 130



February 2010

acceptable leak parameters. As stated above, the acceptable leak rate for the Star Tracker is 2 x 10

-6

sccs, which is a A[Ar] of —35ppm using the model and equations discussed above. Assuming the argon analyzer being used has a relative precision of I% at atmospheric argon concentrations (9300 ppm), the best (1(Y) concentration change that could be observed would be —93 ppm, while a, reasonable confidence level (36) concentration change would be —275 ppm, both of which are inadequate for this application. However, if the ambient argon were removed, the observed leak rate can be reduced significantly, and be directly related to detection limit. For example, an instrument with a detection limit of 10 ppm, could observe a leak rate of approximately 6 x 10 -7 sccs, well within the needs for this application.

A system known as PReLIS, the Portable Leak Indication System, was used for the analysis of the Star Tracker leaks. Mounted on an oscilloscope cart, PreLIS was comprised of a Stanford Research Systems (Sunnyvale, CA) single quadrupole mass analyzer (RGA100), a high vacuum system consisting of an Alcatel (France) ATH 30+ turbo pump and an 84.4 KNF (Trenton, NJ) 4-stage diaphragm backing pump (Figure 31.2.2). Sample acquisition was achieved by direct introduction through an 11-foot, 0.0025-inch I.D., PEEK capillary (Fisher Scientific, Pittsburgh, PA) conductance limit, which also serves as a convenient leak detection sample uptake probe. The system had a 19 — 20 sec response (transport) time as determined by breathing into the capillary intake and measuring the time required for a COZ response. Both vendor provided software and inhouse software developed with LabVIEW (National Instruments, Austin, TX) were utilized. A short Figure 31.2.2 — PReLIS

development time resulted in a software-limited

measurement rate of —9 second intervals for argon and carbon dioxide. The software has since been optimized such that signal-to-noise considerations are now the measurement rate limiting factor, which was about 1 second per scan per ion monitored.

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The leak detection configuration (Figure 31.2.3) had a large, transparent, electrostatic-dissipative, plastic bag placed around the Star Tracker and sealed with Kaptori tape (Torrance, CA.) , with only half of the test article sealed at a time to make it easier to move the probe. A hole was cut into one corner of the plastic bag for connection to the purge inlet line, which was sealed with Kapton tape. Another small hole was cut in the bag near individual test items (valve, electrical connector or chassis seal) while testing. When each individual testing was complete, the hole was sealed with tape, and another hole was cut for the next test item. No specific exhaust hole was created since leakage through the various holes in the bag and the seal around the Star Tracker were considered adequate. Initially, the operator merely observed the raw signal of the mass spectrometer (ion current) while another operator slowly moved the probe around the test article. It soon became apparent that Figure 31.2.3 — Argon Leak Test Setup

monitoring ion current peaks with no reference to actual

gas concentration created a tedious work condition, since not having found any leaks yet, it was difficult to quantify the progress of the leak testing. As a result, a semi-quantitative calibration of PReLIS was performed with a two-point calibration curve using the assumed atmospheric concentrations of argon (9,340 ppm) and carbon dioxide (380 ppm), along with the assumed concentrations of the purge (99.99% nitrogen and no measurable argon and COz contaminants). This linear calibration method is given in Equations 31.2.7 — 31.2.9. Although this calibration method has its flaws and inaccuracies, as a metric for operators to use as a guide during leak testing it proved invaluable.

m = [Ar ]air — [

Ar ]p„rge _ (9340 — 0)ppm

1 Ar,air — I Ar,purge b

[Ar]air — m1Ar,air

36 of 130

(31.2.7)

1 Ar,air — ]Ar,purge (31'2'0)


Âr^ L 1 Samp le

— [Arl air — [ Ar I purge (I — I

I Ar,air

February 2010


Ar,Sam !e + I Ar,air )— Âr^ air p

=

I Ar,Samp[e + I Ar,alr

x 9340 ppm (31.2.9)

I Ar,air — I Ar,purge

Ar,purge

100

90

80

First Pass Inside of Purge Valve

c. 70 c w

Continued Leak Inside Purge Schrader Valve

60

L C

50

v

c j 0

Second Pass Inside of Purge Valve

40

0

30

20

Torque to 4 in-lbs

Base of Purge Valve

10

15:54

^^Jj S

-

0 -

15:59

16:03

16:07

16:12

16:16

16:20

r -O%P%

16:24

16:29

Time, HH:MM (EDT) Figure 31.2.4 — This plot shows leak analysis of the Purge valve.

During leak testing, only two leak points were identified — the Fill and Purge Schrader valves. Figure 31.2.4 shows the argon single ion monitoring plot as the Purge Valve was investigated using the sample uptake probe. Notice that after the first pass of the purge valve, several features are observed. Most importantly is that the signal is much higher than the baseline, providing a high degree of confidence that a leak has been found. Next, the probe was removed from the valve for a period of time, allowing for the signal to return to baseline, then the probe sampled the valve again with similar results. The first, and least evasive, method chosen to fix the leak was to verify that the valve was installed to the proper torque level. Following this effort, leak analysis was once again performed, and it was again shown to 37 of 130



February 2010

leak. Analysis of the Fill Valve (inset of Figure 31.2.3) gave similar results, where inside the valve produced argon peaks of nearly 30 ppm, while the base of the valve showed no leak. With this data, the decision was made to replace both Schrader valves, and subsequent testing showed no argon leaks.

The method presented here demonstrates a technique for locating leaks from pressurized components. Using a plastic bag to create an atmosphere without the leak tracer, argon in this case, a small probe was moved around the test article to identify localized leak points. A model was also presented here to assist in designing the experiment and interpreting the data. In fact the model proposed that a leak signal of nearly 1400 ppm would be expected, however the largest signal observed was an order of magnitude less. This illustrated a significant short-coming in this leak detection method. Although this method required minimal instrumentation and infrastructure and was easily implemented, it cannot account for the situation of multiple small leaks that could exceed the required leakage, nor can it certify a test article to meet an overall leak integrity. Such an application will be presented in the next section.

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31.3 Real-time Leak Detection during Spacecraft Launch Activities

The Space Shuttle uses liquid hydrogen (LH2) and liquid oxygen (LOx) as propellants, which represents a flammability hazard. A nitrogen or helium purge is used to remove contaminants as well as to dilute and vent leaking vapors when loading the Shuttle with these commodities. The sampling of the controlled vent of this purge provides an excellent means to determine the leakage level of various systems during launch operations. An illustration of the primary sections of the Space Shuttle, with the purge monitoring of the Aft, Payload Bay, Mid-body and Inner Tank being the focus is shown in Figure

31.3.1.

Payload Bay

Crew Cabin

AAnn

o

l

^C

aQ

s

r , ^ ~ q

Mid-body Liner Tank

Hydrogen Tank

.-! =

>

Figure 31.3.1 — Illustration of Different Purged Cavities within the Space Shuttle A model is presented here (Figure 31.3.2) that depicts leak testing under closed / controlled conditions. This. model is simpler and more accurate

Vent

than that of a leak into an uncontrolled environment, since all parameters entering and exiting the system can be

QLeak Sensor

measured. Typically the entering (purge) flow rate (Qpurge), pressure and temperature are known and well controlled during an operation. As

P caV" V ca-VI T, I'%"

such, the calculations are given below.

Figure 31.3.2 — Model of System Leak within Purged Cavity 39 of 130

By definition, the measured gas


February 2010


concentration (v/v) is the ratio of the gas volume contribution due to the leak and the total volume. This assumes that the purge does not contain any of the leak commodity, such as hydrogen or oxygen, which is generally accurate, but if not, the leak rate derivation is similar. Assuming the pressure and temperature of the leak gas and pure fzas have equilibrated, which is usually accurate at the point of VLeak

[Gas]=

VPurge + VLeak

=

nLeak

npurge +

=

n Leak

QLeak

QLeak — [Gas] QPurge + QLeak

[Gas]' Q Purge QLeak —

(31.3.1)

QPurge + QLeak

1— [Gas]

( 3 1.3.2)

(31.3.3)

analysis, the volume ratio is equal to the molar ratio. Assuming a homogeneous mixture, the molar flux (flow rate) ratio is equal to the molar ratio. These are described in Equation 31.3.1. Rearrangement yields Equations 31.3.2 and 31.3.3, allowing calculation of the leak rate.

An example of a purged cavity at unacceptable leakage conditions, due to flammability hazard and loss of commodity, is with a measured p urge rate of 3900 scfm. (110,454 sL-om) and a hydrogen leak rate =

QLeak

[H21 J QPurge + QLeak

=

2.34 scfm = 6 x 10 -4 = 600 ppm 3900 scfm + 2.34 scfm

(31.3.4)

of 2.34 scfm (66.3 sLpm). Using the equations given above, the resulting hydrogen concentration would be about 600 ppm (Equation 31.3.4). Monitoring for concentrations in this realm are somewhat commonplace, however, notice that a 251) p m si g nal (near the detection limit) represents a leak rate of -6

Q Leak —

[H 2 ] • QPurge — [25 x 10 1 . 3900 scfm — = 9.75 x 10 -2 scfm 1-[H2] 1— 25x10 6

(31.3.5)

0.0975 scfm (2.76 sLpm), which is still a sizable leak when one considers that launch processing can last up to 12 hours and some commodities, such as fuel cells, have minimal cryogenic tank capacity that must last several days.

For purge gas, leak monitoring during Shuttle launch operations, a mass spectrometer-based leak detection system known as the Hazardous Gas Detection System 2000 (HGDS 2k) was developed [31.3.1]. The primary reason amass spectrometer was chosen for this application is its excellent

40 of 130



February 2010

— 275 FT

—'

detection limits, accuracy over a wide dynamic range, and the capability to monitor and differentiate several species. Mass spectrometers are also unique in their ability to measure trace to bulk levels of helium in a multi-component

XTIJI

system. With detection limits in the 10 ppm range and nearly 5 orders of dynamic range, the system

2

can monitor a variety of launch operations

3

!

a

including propellant (liquid hydrogen and liquid

Sample Lines

oxygen) fill, propellant vent, propellant drain, fuel cell load and several pressurized gas (nitrogen and helium) operations. However, due to the delicacy

and acoustic stresses of launch, the system was

Z11\

ruggedized in a 24-inch component rack and

Figure 31.3.3 — Purged Cavity Sample Lines and

of the mass spectrometer relative to the vibrational

located inside an environmentally controlled area

HGDS 2k System

of the Mobile Launcher. Unfortunately, this mandates the use of several long distance, vacuum, sample transport lines (up to approximately 115 m [370 ft]), which due to the distance and flow rate, results in 15 to 30 second transport times. Samples of purge gas are taken from various locations in and around the Space Shuttle during propellant loading operations, prior to launch, as illustrated in Figure 31.3.3.

The HGDS 2k (Figure 31.3.4) consists of three racks of equipment and is installed into a Mobile Launcher where it is attached to 8 shared, continuously-pumped, sample lines; 7 shared, auxiliary, round-robin, sample lines and a redundant set of 12 calibration lines. The middle rack is a shared gas

41 of 130



February 2010

transport system whereby samples are drawn by oil-free, vacuum pumps to deliver gas samples

--------------

Î

to the active, pressure-controlled inlets of two independent mass analyzers. The two outer

ê

I

r

racks house redundant computer controlled mass

y..

analysis detection systems, each capable of monitoring gases in helium, nitrogen, or air backgrounds. Each mass spectrometer enables near-simultaneous (within 2 to 8 seconds) monitoring of all gas constituents of interest, t

range, maintains 10% accuracy over 5 orders of

i

Figure 31.3.4 — Photo of HGDS 2k prior to installation in Mobile Launcher

achieves detection limits in the 10 to 25 ppm

dynamic range; all with an internal system response time of less than 10 seconds.

The mass spectrometer is based on a low cost, open-source, linear quadrupole [31.3.2] residual gas analyzer from Stanford Research Systems (Sunnyvale, CA). Both Faraday cup and electron multiplier detectors are available, although the multiplier was used here. The mass analyzer generally operates in single ion monitoring mode, with the typical configuration monitoring hydrogen, helium, nitrogen, oxygen, and argon at mass-to-charge ratios of 2, 4, 28, 32 and 40, respectively. An Alcatel 31+ turbomolecular-drag high-vacuum pump was utilized for its ability to operate in high oxygen and water environments along with the need to monitor hydrogen and high levels of helium. The Alcatel model was chosen due to its high compression ratio (10', 10 7 , and 10 for H2 , He and N2, respectively), which allows for improved response and recovery times relative to other high vacuum pumps. For this application, the system operates best when the analyzer is in the low-10 -5 torr pressure range.

To complement the two independent analyzers of the HGDS 2k system, a separate set of NIST certified [31.3.3] calibration gas mixtures are installed on each side of the sample transport system. These calibration gases are plumbed directly into the sample system, such that an operator can switch (local or remotely) from a sample line to a calibration line at any time. The calibration gases serve two purposes. The primary function of the calibration gases is to provide a means to generate a calibration curve for 42 of 130



February 2010

the system so that in real time an operator can have data provided in terms of raw response (pico-amps in this case), or in terms of relative concentration, such as parts-per-million The secondary function of the calibration gases is to serve as an immediate comparison when an event of concern occurs. Such a comparison provides good evidence that HGDS 2k is functioning properly and that an event has occurred. This reduces the high rate of false readings that plague so many harsh environment sensors. In fact this method of comparison, and the excellent observation skills of the operators, was successfully used to identify a false negative event during launch processing [31.3.4].

Two types of computers control HGDS 2k - local and remote. The local computer controls all hardware functions and interfaces to the remote computers. The remote computers provide user interfaces and most data logging. The local system is a VME platform computer that interfaces with all hardware systems via serial RS-232 communications. These systems include the RGA, turbo pump, pressure transducers, flow meters, and flow controllers. Analog and digital inputs and outputs also communicate via RS-232 across an OPTO-22 (Optomux) bus. The local computer system is part of the redundant outer racks comprising HGDS 2k. The local system interfaces with up to eight remote computers via a fully redundant Ethernet 100 BaseT. All data is time-tagged locally using an IRIG module within the VME chassis. The remote personal computers use a Microsoft operating system with user interface software written in C++. The software enables the user to input all commands and to monitor the health and the status of the system. All calibration, tuning, and gas concentration monitoring is performed by sub routines, or windows, written specifically for the task. The interface is considered intuitive and easy to operate, thus allowing engineers from various backgrounds to learn the system with minimal training. The software has been revised several times to provide additional operational features such as scripting and improved data visualization and analysis capabilities.

Three NIST traceable (secondary standards) calibration gas bottles [31.3.3] designated Low (99.9999+% N2), Test (500 ppm H2, 500 ppm He, 500 ppm 0 2 , 100 ppm Ar, and balance N2, nominally), and Span (5000 ppm H2 , 5000 ppm He, 5000 ppm 0 2, 1000 ppm Ar, and balance N2, nominally) were analyzed sequentially for total duration of about 7 minutes. Each gas bottle is selected for 60 seconds to allow the system to equilibrate, then 10 data points are collected, at which time the next bottle is selected. This constitutes the calibration cycle, where data from all three bottles are used to determine a three-point least-squares calibration curve and the test bottle also is used to assess the quality of the calibration. 43 of 130



February 2010

Using the 10 data point, averaged measured ion response for the gases of interest for the Low gas (XL), Test gas (XT) and Span gas (Xs), and the certified calibration bottle concentrations for the Low gas (CL), Test gas (CT) and Span gas (Cs), the sensitivity coefficient (m) and offset (b) are calculated using M—

3(XL CL +XT C,. +XS CS )— (XL +X,. +XS XC, +C,. +CS) 3 X, + X + XS — ( X, + X,. + XS )z

b = 3 (C, +CL + CS) — 3 (XZ +X, +XS )

(

31.3.6 )

(31.3.7)

Equations 31.3.6 and 31.3.7, respectively. To obtain a measure of the quality of the calibration, a calibration error is calculated by determining the relative error between the measured Test gas concentrations, using the calibration curve, and that given by NIST analysis (Equation 31.3.8). A relative accuracy of 10% is considered acceptable for this application. Once the calibration has been %oError = (mX

TC b ) — C,,

X100%

(31.3.8)

T

completed, and the accuracy requirements are met, the Equation 31.3.9 is used to calculate the concentration of the sample (C, mpi) using the sensitivity coefficient (m), offset (b) and the measured sample response (X,,,,pi). It is interesting to note that when operating this system near the detection

CSmpr = m - X s,,;P,

+b

(31.3.9)

limits, a 3-point calibration actually provides ±10% analysis accuracy over a broader concentration range when compared to using 4 or 5 point linear regression calibration curves.

Although an accuracy requirement of 10% may seem trivial for many analytical techniques, it is a realistic goal for this application considering the concentration range (ppm to percent levels) and the sample type (permanent gases). The system was originally designed to maintain the 10% accuracy level for only 12 hours, however it has been demonstrated to maintain this accuracy level for several weeks when retained in an operational state.

44 of 130



February 2010

-I-1X11 Ges DPA

I

6at PafCent

I Wi

Ion Qurrent

I two ororsure

I

L o

I

I

flow Sa le Mas s TW

I tuft Nv I _140

-140

-120

-+00

_80 1 -60

-40

-

20

-0 1

1515

I

15:25

7520

--2p

1530

1540 ISIS CWT C1t NN, 60 h+ARe hdory)

1576

EVtnts W Plot F Tr4a 15:27:50 Cww l, I"

Cursor ;tr 001911r+5:S3 ;5

1550

+556

(was ON, T- ; t • ;

iw

16.06

1600

c,*,,

Stalm4 r Auto

1610

- 15.0 to 200.0

HSr drogrn

Hplium

NW01g"

ormn

ArhMOMA

H2O

Null

Poo

172.E

PPM

PD N

OON

I . n

WN

5:.6

Df/*

DON

DDN

Aq

170.8

AYQ

Ave

Avj

-I.8

Avg

55.5

Avg

r - Hat

r Rot

= .1

I^.t Coen" Iro AebRr

r

PW

- _._

5W(* Row

Argon

r Rot

Srr%* P1 inure

J

r Rot

Avg ^J

twGO"SPW

I

Ave

r Pw --

J'Â'

J

r Pw

PoMS for A.4W

S

l

4 t59f16.1D:10

Figure 31.3.5 — Data from a nominal hydrogen leak during propellant loading for STS-111.

Data analysis was perform in real time by the software running on the remote computer. Once a calibration has been performed, the software retains the calibration parameters and converts the measured raw signal (ion current) into the calculated gas concentration. An example of one of the primary user interfaces is shown in Figure 31.3.5. The screen shot shows the historical data plot for hydrogen (top plot on right side), argon (middle plot) and oxygen (lower plot on right side). Other accessible information in data boxes or on header taps include instantaneous gas concentrations and a variety of other system parameters such as current sample line, sample flow, and sample pressure. The window tabs can be selected to view historical data plots of the raw, ion current data as well as a wealth of health and status data. Notice that the screen shot also shows when the calibration gas was activated (15:25 GMT), as a means to both confirm that the upward hydrogen trend was accurate, but to validate the accuracy of the hydrogen data. 45 of 130



February 2010

On several occasions, HGDS 2k has identified or verified leak conditions during launch operations that could have resulted in equipment damage, mission failure or loss of life. Mass spectrometry has proven to be an excellent technology to use for leak detection during cryogenic propellant transfer.

31.4 Post-launch Analysis of Engine Performance and Integrity

The stresses on the Space Shuttle Main Engines (SSME) during launch are of concern because of the harsh vibration and acoustics experienced by the vehicle during accent to orbit. This is of utmost importance for the Shuttle because of the humans aboard the vehicle and the fact that the SSMEs are reused. As was discussed in earlier sections of this chapter, extensive leak checks are performed before launch. Because of the volume and safety concerns associated with liquid hydrogen and liquid oxygen propellants, testing of the engines are performed utilizing helium or other tracer gases. While the leak checks have proven to be a viable method to characterize the SSMEs, many factors keep them from being a complete picture of the SSMEs' state during launch. The two major factors that limit this method of leak detection are the inability to use liquid hydrogen or liquid oxygen and that the engines are not operating during the tests (low pressure). Therefore, it is important to have some means to determine if a major leak of the SSMEs has occurred during launch. Toward this end, a method was developed to examine the gases in the Aft Compartment during ascent. Detecting an anomaly during launch involves monitoring the same compounds as before launch (H 2, He, 02, Ar) plus new targets: CO, CO 2, and low molecular weight hydrocarbons. The CO and CO2 are mainly utilized to determine if the exhaust from the pyrotechnic devices on the sample bottles was pulled into the sample bottles and thus interfering with the analysis. The method that was developed involves acquiring samples during launch and analyzing them post landing, after the vehicle is back at Kennedy Space Center, FL. While the pre-launch leak tests are interested in extremely small leaks, equating to parts-per-million concentrations, these analysis are interested in larger leaks, equating to percent concentrations. However, unlike ground processing, this technique requires the analysis to be performed at multiple sub-atmospheric pressures because samples are obtained as the vehicle ascends 46 of 130



February 2010

and the atmospheric pressure decreases. Meeting these requirements meant that not only did unique instrumentation need to be implemented but also that new sample catch bottles had to be developed.

The overall methodology for these analyses is a rather standard approach to sampling and analyzing samples. The samples are collected into sampling containers, or bottles, and transported back to the laboratory where the analysis is performed. The analysis utilizes a uniquely designed gas chromatography/mass spectrometry (GC/MS) system. Mass spectrometry was determined to be the best detection system for this application because of the need to monitor helium and other constituents that would require a large sample to feed multiple analytical techniques. Mass spectrometry is also very sensitive, needing only a small sample for analysis. Gas chromatography was utilized to separate the components from each other, thus helping to eliminate interferences that occur when MS alone is utilized. The combination of the GC and MS techniques provide two parameters (retention time and mass spectrum) to confirm component identification. This double confirmation is important because erroneous measurements could lead to very costly and/or potentially deadly mistakes during Space Shuttle processing. For example, a false positive report of a leak would lead to extensive amounts of money (millions of dollars) and launch schedule delays. However, the worse case would be a false negative report that could lead to a catastrophic leak occurring during operation and either cause an abort during the mission or the loss of the vehicle and crew.

While the sampling technique followed a relatively standard methodology small, rugged, lightweight sample, or catch, bottles had to be developed. The catch bottles have to be able to sit on the vehicle ready to support launch for a month, autonomously collect a sample, hold the sample for up to a month without degradation, withstand launch vibrations, and be light weight. The current design of the sample bottles are shown in Figure 31.4.1. These sample bottles are made out of aluminum, have two pyrotechnic plugs, a sampling port, an evacuation/monitor line, and a location for the attachment of a cold cathode gauge to monitor pressure. Before reuse the bottles are sent to the manufacturer and totally refurbished. This includes complete disassembly, reassembly, bake-out, and leak checking. In addition to the refurbishment, the bottles are evacuated to less than 1 x 10 -7 Torr; they typically arrive with pressures below 1 x 10-8 Torr. Extreme care is taken to clean the bottles and ensure no contamination or residual atmospheric gases are present; this is critically important because of the low pressures of the

47 of 130



February 2010

samples and because some of the most important components of interest are the same, or similar, to commodities naturally occurring in the atmosphere

(not installed for flight)

Sample Port (b)

Figure 31.4.1 — Side and top views of the collection bottles; the device on the copper tubing on the left of the figure is the interface valve used to attach the unit to the GC/MS introduction system and puncture the copper tubing. The interface valve is not attached during flight. The samples are introduced into the bottles by firing of the pyrotechnic valves (a) which allows the surrounding atmosphere to enter the sample port (b). After two second the adjacent pyrotechnic valve fires (a) sealing the sample inside the collection bottle.

After refurbishment the bottles are sent to KSC to install onto the Orbiter before launch. Three sample bottles are then assembled onto mounting racks; these racks are used to mount the bottles to the Orbiter and to feed the pyrotechnic control lines to the correct locations. One rack assembly, containing three 48 of 130



February 2010

bottles, is mounted on each side of the Aft Compartment. If the launch is scrubbed and a delay occurs for an extended period the pressures are re-verified before launch; it is not necessary to dissemble the mounting racks to measure the bottle pressures.. This is accomplished via a cold cathode gauge located below the copper tubing; the magnets and high voltage leads are slipped over the gauge on the bottle.

At specific times during ascent the sample valve on a bottle is opened for one second; this is accomplished by firing one pyrotechnic valve which allows gas to enter the bottle through the sample port. The second pyrotechnic valve is fired two second after the first; closing the valve and trapping the sample inside of the bottle. After firing the pyrotechnic valves must be able to withstand the shock of re-entry, landing, and a possible ferrying flight without allowing any atmospheric gas from entering the bottle.

After landing the catch bottles are sent to the laboratory for analysis. In the laboratory the catch bottles are attached to the GUMS via the monitor line. After the bottles are attached to the instrument the sample lines are evacuated and leak checks are performed. The gas samples are analyzed sequentially by puncturing the monitor line via the hand valve which allows the sample to enter the GC sample loop. The pressure is recorded after a stable pressure is reached and the sample is injected onto the GC for analysis. The monitor line is then reclosed via the hand valve and the GC sample line is evacuated for the next analysis. Each catch bottle is analyzed three times and the average reported. The initial pressures of the sample bottles are calculated utilizing the ideal gas law. Where Po is the pressure in the catch bottle before the sample is removed, Vo is the volume of the catch bottle, P, is the pressure in the catch bottle when opened to the sample line, and V, is the total volume of the catch bottle and sample line. POVO = P, V,

(31.4.1)

Rearranging gives Po

= V V 0

(31.4.2)

The pressure for the second replicate gives the following equation, knowing that the volumes do not change during the processes. Where P 1 is the pressure in the catch bottle when opened to the sample line the first time and Pz is the pressure in the catch bottle when opened to the sample line the second time. 49 of 130



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P — V,

(31.4.3)

Po = P, fl-

(31.4.4)

P2

V2

Substituting into Equation 31.4.2 gives

P2

This method does not require knowing the volumes of the sample lines or the catch bottles; thus allowing the modification and repair of the sample system without the need to validate or verify the sample volumes.

The samples are analyzed by a uniquely designed GUMS to enable the monitoring of mass-to-charges (m/z) 1 to 50 amu with sample pressures ranging from 2 to 200 Torr. A one point calibration, acquired at around the same pressure as the sample, is utilized to determine the concentration of the unknown sample. The flow schematic of the GUMS and sample introduction system is shown in Figure 31.4.2. The design allows the standard gas to be introduced from a high pressure bottle into the low pressure collector (A); this pressure is adjusted to be comparable to the expected sample pressures. To perform the analysis, the entire delivery line, including the sample loop, is evacuated by opening valve "Ext B Vacuum On/Off' and the valve "S" corresponding to the sample to be analyzed, Figure 31.4.2(a). After 10 minutes, valve "Ext B Vacuum On/Off' is closed. The Interface Valve on the bottle, Figure 31.4.1, is then used to introduce the gas into the sample loop. After the pressure stabilizes, the Interface Valve is closed. The sample is then introduced into the GUMS via valve V-1, Figure 31.4.2(b). The GC utilizes a Carboxin column for separation of the different compounds. The Carboxin Column separates all of the compounds except for oxygen and argon and this highlights the advantage of a mass spectrometer detection system over other detection methods: to deconvolute this type of GC coelution.

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Figure 31.4.2(a). Flow diagram that depicts filling the 100 µL sample loop from the collection bottle attached to inlet S-3.

The resulting chromatograms, acquired during analysis, are then automatically processed to determine the peak height of the compound of interest utilizing the Varian MS Workstation Version 6.4.1 Software and this information is saved as an ASCII file. These ASCII files are processed with a LabView program, written in-house, that calculates the unknown concentrations and then writes the data to a table that is imported directly to the final report. This method removes the need for repetitive operator steps, which eliminates typographical errors. After the data table is produced the data is reviewed to check the validity of the data; to determine if any points are outliers or have large standard deviations. This step is useful to determine if any particular point needs closer examination. Even though the data analysis is performed automatically, a skilled knowledgeable operator is needed to review the data. Once the data is collated and reported it is sent to the modeling group to for further analysis. The data is used to 51 of 130



February 2010

determine the probable rate that the engines leaked during ascent. It is impossible to make a system that does not leak. Therefore modeling of the data is important to observe if anything unusual occurred during operation and to obtain a trend of how the engines behave during operation.

Figure 31.4.2(b). Flow diagram that depicts injection of the sample into the GUMS for analysis.

31.5 Gas Analyzers for Metabolic and Physiological Experiments

The Mercury and Gemini programs demonstrated that man could survive launch accelerations and work efficiently in the microgravity environment of a spacecraft. Although on orbit physiological 52 of 130



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measurements were obtained during these programs to verify crew health and inflight performance; detailed medical investigations were relegated mostly to postflight evaluations. 31.5.1] The trend of limited medical studies on orbit continued through the Apollo program with collected medical data concentrated on understanding the physiological responses that would have the greatest impact on crew health and safety.

Data from groundbased bedrest studies, which simulated living in a microgravity environment, showed a decrease in work performance. [31.5.2-5] Supporting the bedrest study trends, it was found in the Apollo program that most astronauts had a reduced tolerance for exercise during a period of hours after landing. [31.5.6] This effect was not observed during the Gemini program, because the post-flight assessment occurred —24hrs after landing; by which time the astronaut had readapted to Earth's gravity. In the mid-1960s, NASA recognized the need to perform extensive on-orbit medical investigations to accommodate longer stays in space if exploration was to continue. Skylab (originally the Apollo Applications Program) was the logical follow-on to the Apollo program. The Skylab medical experiments included cardiovascular, musculo skeletal, hematological, vestibular, metabolic, and endocrine investigations. [31.5.7] The work begun on Skylab has continued on the Shuttle's Spacelabs, Shuttle-Mir, and ISS. This section will focus on the mass spectrometers used for metabolic studies on Skylab, Shuttle and ISS.

The performance decrements observed in the Apollo program were reversible within a day or two, but the possibility existed that longer durations in space might lengthen the recovery time or produce an irreversible effect. Therefore, the M-171 metabolic experiments [31.5.8] became a key investigation in to whether humans could adapt and work for long periods of time in a space environment. The primary goal of these experiments was to determine if the decrement in performance progressed with increasing length of microgravity exposure and what effect, if any, on orbit exercise might play in mitigating the reduced performance A secondary goal was to test the bicycle ergometer as a personal exerciser. The equipment suite for M-171 contained the first mass spectrometer to be used on a manned spacecraft. This mass spectrometer was the metabolic gas analyzer system (MGAS), which measured the gases in the exhaled breath. This information was used to derive the crew's level of performance when exercising.

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Metabolic experiments continued during the Shuttle program, where the emphasis turned to defining the most effective countermeasures to combat the temporary performance degradation on an astronaut's return to Earth. Most experiments were performed on the Extended Duration Orbiter (EDO) missions, which as the name implies, lengthened nominal Shuttle missions from 5 days to as much as 16 days. [31.5.9] Objectives of experiments were to assess the effect of different types of exercise, the intensity of the exercise, and the timing of the exercise (i.e., intense exercise near the mission's end). Although many of the Shuttle experiments used only preflight and postflight data [31.5.10] a modified version of the Skylab mass spectrometer (Gas Analyzer Mass Spectrometer-GAMS [31.5.11 ] and later a new quadrupole mass spectrometer (Gas Analyzer System for Metabolic Analysis Physiology-GASMAP [31.5.12] were used in some investigations.

Similar experiments to those performed on Shuttle [31.5.13 and 31.5.14] occurred during the ShuttleMir missions [31.5.15], but with the launch of ISS, it became possible to conduct more extensive studies, because the metabolic experiment's equipment suite was included in the permanent Human Research Facility (HRF) rack. [31.5.16] The GASMAP from the Shuttle missions was used in the ISS experiments, which performed periodic assessment of crew aerobic capacity by analyzing human metabolics, cardiac output, lung diffusing capacity, lung volume, pulmonary function and nitrogen washout. Additionally, another set of experiments examined the effect of long-term exposure to microgravity and extravehicular activity (EVA) on pulmonary function by studying crewmembers before and after an EVA. Combined, these experiments examined whether pulmonary function was affected by long-term exposure to noxious gases or to particulate matter that may accumulate in the atmosphere of ISS. [31.5.17]

The MGAS and GAMS were derived from the Perkin-Elmer two-gas analyzer design developed for Langley Research Center [3.1.5.18] The mass range, and hence the number of target compounds, was increased from 50 amu in the MGAS unit to 120 amu for the GAMS. [31.5.19] The Skylab experiments required detection of low molecular weight compounds at high concentrations (% level). The final version was a single-focusing 90° magnetic sector mass spectrometer, which used a metal sintered molecular leak to sample gases and dual heated filaments as the ionization source. [31.5.20] Ion collectors produced signals for oxygen, nitrogen, carbon dioxide, which were converted (details in section 31.7) to currents, then summed and compared to total pressure (Figure 31.5.1). An internal ion 54 of 130



February 2010

pump maintained vacuum with a sealed gas analyzer assembly. Computation for deriving the data was performed onboard by the MGAS' analog computer.

Figure .31.5.1: MGAS mass spectrometer Measurement accuracy (Table 31.5. 1) was maintained through the use of a hand pump and pressurized canisters of known gas mixtures. Calibrations were performed prior to launch, during the activation of the Skylab laboratory on orbit, and at the beginning of each Skylab mission. Results from the calibrations showed that the MGAS remained stable throughout the entire Skylab program. The gases of primary interest for the exercise decrement studies were oxygen and carbon dioxide from which, along with other measurements the metabolic pulmonary function was derived.

Table 31.5.1 —MGAS Accuracy Requirements Target Component Nitrogen (`2) Oxygen (02) Water (H2O) Carbon Dioxide (CO 2) Hydrogen (H2)

Maximum Partial Pressure Torr 660 330 33 23.1 3.3

Accuracy %FS 2 5 3 20

Maximum total pressure: 800 torr

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ttten/m1n1

4. 0

1 STANDARD DEVIATION 200 q PREFLIGHT ® IN-FLIGHT 190 q POSTFLIGHT 180

1 + _ 'STANDARD SiPO StsW ira teênture;

Preuure•dry

DEVIATION PREFUGHT ® IN-FLIGHT

3.0

170

0 POSTFLIGHT

V.02'

160 HEART ISO

RATE, 140

.STPD

130. 120

i r I 3:

2.0

110 100 90R

80.

5

7 s

568

SPY CDR PILTCDR SPY . FLY SKYLAB 1/2 I SKYLAB 3

1.0 CDR .I

SPY PLT" SKYLAB 4

. CDR'

SPY

SKYLAB 2

CDR

PLT I

SPY

PLY

CDR

SKYLAB 3

SPY

PLY

SKYLAB 4

'SIGNIFICANT DIFFERENCE FROM.BASELINE ip 0.051

'SIGNIFICANT DIFFERENCE FROM BASELINE Ip 2 0.05)

Figure 31.5.2 — Heart Rate

Figure 31.5.3 — Oxygen consumption

The aerobic capacity of each crewman was determined approximately 12 and 6 months before their mission, and based on this data the an inflight protocol was derived for each crewman. The protocol required data acquisition during specified exercise periods (25-75% of maximum oxygen uptake- Voz) and during rest. [31.5.21 ] This experiment was conducted approximately every 4 to 6 days on orbit. The results for the three Skylab missions (Skylab 2: 28 days, Skylab 3: 59 days, and Skylab 4: 84 days) are shown in Figures 31.5.2 and 31.5.3. Combined, these graphs show a postflight decrement in response to exercise as indicated by the decreased oxygen pulse (increased heart rate for the oxygen consumption). Experimental data showed that all Skylab crewmen experienced a significant postflight decrement in submaximal exercise response. The Skylab 2 crewmembers, who exercised less than Skylab 3 or 4 took 18 to 21 days to readapt. However, the crewmember from Skylab 4, who exercised the most, only required 4 days to recover. This experiment demonstrated that there was a direct correlation between extensive exercise on orbit and a short recovery time when returned to Earth. Length of stay in microgravity was not a factor in readaption time, if exercise countermeasures are employed. The GAMS unit (Figure 31.5.4 and 31.5.5) used the same basic configuration as the MGAS, but with several design improvements, including the extension of the mass range 120 amu. The GAMS also increased the number of compounds measured to nine (nitrogen, oxygen, carbon dioxide, water vapor, isotopic carbon monoxide, nitrous oxide, argon, helium, acetylene, and total hydrocarbons (m/e 50-120).. These changes were required as the investigations expanded to more detailed metabolic studies. 56 of 130



February 2010

^.^,^ f.+

(

i

OPERATION

_

^

ru,.

^

xm 6 months) crew stays on orbit, and 2) the facility was to conduct a large number of scientific experiments and advanced hardware system tests. Experience from the Skylab [31.7.13] and Shuttle programs [31.7.14] and later confirmed during the Shuttle-Mir project [31.7.15], predicted that there would be air quality degradation events on ISS. These events might include leaks or spills from systems and payloads, overheated wiring and electronics, and failures of scrubbers recycling the air. The Shuttle-Mir program incidents showed that periodic archival sample return was not always adequate to address air quality issue on long-term spacecraft missions. A volatile organic analyzer was proposed as a real-time volatile organics (VOCs) monitor to complement archival sample returns from ISS. As stated in section 31.1.2, the Volatile Organic Analyzer (VOA), based upon gas chromatography- ion mobility spectrometry (GC/IMS) was selected as the first instrument to measure trace VOCs in near real-time onboard a spacecraft. In the mid-1990s, NASA created the ISS risk mitigation experiments (RME), which used the Shuttle to assess the performance of complex operational hardware in microgravity. In microgravity there is no thermal convection, so it was unknown whether the heating and cooling of components (i.e., GC column) could be accomplished with the precision required to meet the VOA Figure 31.7.8 — Astronaut Bonnie

instrument performance requirements. The VOA risk

Dunbar operating VOA/RME on STS-89 mitigation experiment (VOA/RME) was flown on two missions: STS-81 and STS-89 [31.7.16]. The VOA/RME contained a cylinder of carrier gas (nitrogen), which resulted in a two-box configuration (Figure 31.7.8). These were the only differences between the VOA/RME and the planned VOA. Results from multiple uses of the VOA/RME will be discussed later in this section.

The VOA was sent to ISS in August of 2001 and operated there until August 2009, with an inactive period from 2003-2005. A potential replacement for the VOA was flown to ISS in May 2009 as an

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February 2010

experiment and a discussion of this instrument, gas chromatography/differential mobility spectrometry (GC/DMS), will appear at the end of this section.

The VOA is composed of two channels, each having an inlet, a gas chromatograph (GC) interfaced to the detector (ion mobility spectrometer), pumps, and a controlling computer. A block diagram of the VOA is shown in Figure 31.7.9. The two channels provide almost redundant function if only one channel is functional. The VOA's pump pulls an air sample through two preconcentrators containing Carbotrap B and Carboxen 569 sorbents, which extract and concentrate most VOCs of interest. Heating the preconcentrators, with a flow of nitrogen gas, sends the VOCs to GC columns where the complex mixture is separated. The detectors are ion mobility spectrometers (IMS) that identify and quantify the compounds as they elute from the GC column. [3 1.7.17]

Figure 31.7.9 — VOA block diagram

Each detector responds to positive and negative ions, but not simultaneously; therefore two complete runs (Parts 1 and 2) are needed for each analysis. Two Quadrex stainless steel capillary columns are used: Channel 1 is a 60m x0.5mm 1.5m UAC-5 (5% phenyl 95%methyl silicone) which separates nonpolar compounds and Channel 2 is a 60m x 0.5mm 2m UAC-502 (cyanopropyl methyl phenyl silicone) for polar compound separation. The GC and heater were coiled and layered around a metal former (25mm bore) resulting in temperature reproducibility better than ±I'C. The detectors in the VOA determine the GC retention times and the ion mobilities for target VOCs, which it uses to provide accurate compound identification. The VOA determines the contaminant concentration by comparing the integrated area of the ion mobility peak to a calibration table. Compounds eluting from the GC columns are ionized in the IMS detectors by a 10 mCi 63 Ni source. The ionization is almost exclusively by charge transfer rather than direct ionization [31.7.18]. The ions (either positive or negative) are "gated" into the drift region during a 180us pulse. The ion's mobility is the time needed for it to 80 of 130



February 2010

traverse the detector's drift tube under the influence of a weak electric field, which drives the ions toward the detector against a counter flow of scrubbed drift gas (VOA-air). The ions undergo multiple collisions with the drift gas; therefore its cross-sectional area (size and shape) determines the time required for the ion to reach the faraday cup detector. A faraday cup detector is used to convert the ions into an electrical signal (nanoamps). A biased aperture grid is placed close to the detector to protect it against charge build-up and to filter noise from the gate pulse.

The ion mobility is normalized for temperature, pressure, and electric field strength and is named the reduced ion mobility, k,, (Equation 1). This equation is valid for weak electric fields (-200V/cm in the VOA detectors). Pressure and temperature sensor data are used to normalize the mobility as shown in Equation 31.7.1 and purely for mathematical convenience, the VOA calculates and presents data as the reciprocal of the reduced ion mobility (1/k,,). _ d

P ) ( 273K')

k° E • t 760 torr ko = reduced mobility (cm2V

T

(31.7.1)

"1s_1)

d = drift tube distance: shutter grid to electrometer (cm) t = drift time of ion (seconds) E= electric field strength (V/cm) P= cell pressure (torr) T= cell temperature (K) The IMS detectors always have a standing current (hydronium and oxygen ion clusters in the positive and negative modes respectively) referred to as the reactant ion peak (RIP). Aanalyte peaks are ionized by charge transfer from the RIP ions (Figure 31.7.1 Oa), which decreases the height of the RIP to produce the anayte peak (Figure 31.7.10b). Drift gas scrubbers control the moisture in the ionization and detector regions (—a few hundred ppm), enabling reproducible ion mobilities.

81 of 130


3.3 A 2.7 s = 2.1 rn

February 2010


Mobility Spectrum August 2006

3.3 g

Mobility Spectrum August 2006

2.7

RIP, No analyte present

RIP, No anyt 31 e present

X2.1

L 1.5

Analyte peak

,= 1.5

Y

Y a 0.9 C

v 0 . 9 o.

0.3

0.3

RIP, analyte present i

-0.3

-0.3 0.2

0.3

0.4

0.5

0.6

0.3

0.2

0.7

0.4

0.5

0.6

0.7

11ko

1 No

Figure 31.7. l Ob — IMS response with analyte

Figure 31.7. l Oa — IMS response no analyte

The VOA performs very fast scans over the ion mobility range (0-20ms), then 16 scans are averaged and stored (along with sensor data) every second of the run to produce smoothed spectra throughout the GC run. The RIP (Figure 31.7.1 la) can be plotted (similar to the TIC of MS) with a single ion mobility for specific compounds and multiple mobilities (Figure 31.7.11 b)can be graphed (analogous to SIM in MS). The mobilities for some analyte ions can be in close proximity to the RIP; therefore data processing involves background subtraction of the RIP by software (Figure 31.7.2.1 1 b). 5 —RIP(0. 420mS)

Fik ... I

— 0.502mS

Freon

d

p

o

1/k.0.499

22

> 4

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3

Frroo 113

u ^

2

X

t/k.0.520 1/k.OJ20

o-Xyleoe

nip-Xylme

d Î

0 -1000

0

1000

2000

GC Retention Time (Sec)

3000

Figure 31.7.11 a — VOA spectrum: RIP analyte peaks

Figure 31.7.1 lb — Multiple 1/k,,

Compound identification and quantification is performed on the "charge" area (i.e., peak area) of the analyte's ion mobility peak, not the GC peak.

Pinacolone (3,3 dimethyl-2-butanone) is the calibrant added to all runs as a check on instrument performance. . Prior to sampling, a flow of nitrogen constantly purging the calibrant oven is diverted through the preconcentrator and this adds the pincalone to the preconcentrator. The previously described analytical sequence would begin after the sample is acquired. The calibrant's GC retention time and mobility are verified as correct and the approximate charge area is compared to expected values to insure proper instrument operation. 82 of 130



February 2010

An internal picture of the VOA is shown in Figure 31.7.12. The scrubbers and pumps were orbital replaceable units (ORUs) along with scrubbers for the nitrogen carrier gas, computer hard drive, cooling fan, and inlet nozzle filter (not visible in figure). The two components below the preconcentrators are Sport, 2-position Valco valves (with valve drivers), which were the heart of the VOA's pneumatic system.

Figure 31.7.12 — Internal view of the major VOA components These two valves directed sample, carrier, and purge flows through the appropriate components. All fittings and lines in the sample path were stainless steel and the entire path was heated to avoid losses of polar compounds to the walls. The nitrogen carrier gas was obtained from the ISS tanks as the VOA usage was miniscule. The IMS cells were operated slightly below ambient pressure and a "metered" leak maintained drift gas oxygen levels high enough for effective negative mode ionization. The VOA had a plethora of sensors that monitored temperatures, pressures, voltages, flows, valve position, and current.

The VOC target compounds on ISS were derived after reviewing archival samples from Shuttle and Mir as well as the compounds detected in offgas tests. Compounds frequently detected at measurable concentrations (i.e., acetone), toxic compounds (i.e., benzene) that could be found on spacecraft were added as targets, and compounds (i.e., 2-propanol) that can impact the ECLS systems (water recovery). The original VOA target compound list [31.7.19] was reduced to the compounds shown in Table 31.7.2. Most compounds removed from the original list were those that couldn't easily be chromatographed

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(acetic acid), ones that could not be trapped by the preconcentrator (carbonyl sulfide), and those for which it was impossible to make reliable standards (2-butoxyethanol). The NASA toxicologist

Table 31.7.2 — VOA target compounds (shaded-must detect) and required detection limits Cone. Compound Cone. Compound (m /m3 m /m3) methanol 0.5 (F22) chlorodifluoromethane (or F12) 10 1-butanol 5 (F113) 1,1,2-trichloro-1,2,2- ??? 5 m,p-xylene 10 ethanol 5 5 Benzene o-xylene 0.1 propanone 1 Hexane 5 ethylacetate 5 2-methyl- I ,2-butadiene 10 ethanal 0.5 (Halon 1301) trifluorobromomethane 10 toluene 3 ethylacetate 5 DCM 0.5 2-methyl-2-propanol 5 2-butanone 3 1, 1, 1 -Trichloroethane 1 determined that the compounds removed from the list did not diminish the assessment of air quality by the VOA. The shaded compounds in Table 31.7.2 were those that must be detected, but allowance was made for qualitative analysis of 1 or 2 of these compounds. The VOA had to detect 80% of the remaining compounds. The detection limits shown in Table 31.7.2 were easily met by the VOA with the exception of benzene, which the VOA just met when the sample volume was reduced from 100 ml to 40 ml to accommodate the higher concentrations of other compounds in spacecraft samples. Most compounds are routinely detected below 1 mg/m3on ISS, so the VOA's low detection limits for many compounds were a distinct advantage for the technique.

The VOA's precision requirement is very important, because in a contingency (i.e., fire, spill) the VOA data can be used to determine the effectiveness of clean-up and to add to the pool of information needed to inform the crew when they can remove their masks. For these reasons, the standard deviation for three consecutive VOA runs (clean run in between) could not exceed ±20%. The VOA accuracy requirement was ±50%, which to most seems like a very large allowance. However, consider that the data is compared to the SMACs, which themselves often have uncertainties exceeding ±50%. Secondly, the EPA methods used for analysis allow a deviation of ±25/% and ±30% for a few compounds (i.e., methanol); however the GUMS analysis of the GSCs is considered the absolute 84 of 130


February 2010

Ch 31 - MS in Space

answer and the VOA must be within ±50% of those values. Therefore, the VOA accuracy requirement is tighter than it seems, but more importantly it meets the operational objective: provide the NASA toxicologist the data required to assess the spacecraft air quality. [31.7.20]

The VOA calibration began with the runs of individual compounds to establish GC retention times and ion mobilities, which are the two identification parameters. A database was created and a "large" twodimensional identification window (GC retention time vs 1/k o) was established. The quantitative calibration then proceeded with 40 ml sample volumes of 5 mixtures, at different concentrations, but each containing all the target compounds and run in triplicate. The standards were prepared in 6-L Summa-treated canisters, but aliquots of the mixtures were transferred to sample bags (Teflon) to interface with the VOA for Part 1 sampling. Approximately 1.5 hrs after Part 1, the sample bags were refilled for Part 2 (detector polarity was reversed on each channel) sampling of the VOA analysis. The GC retention times and 1/k o from these runs are used to firmly establish the identification windows. The analytical runs can be reprocessed by Trimscan (vendor supplied software) if the database is altered. It is imperative that these two parameters be reproducible and Table 31.7.3 shows data from VOA's instrument calibration that demonstrates its excellent performance. The VOA's two-part analysis took approximately 3.5 hours. Table 31.7.3 - The percent relative standard deviation of the GC retention times and 1/k os for the VOA target compounds. These data based upon runs of mixtures at 5 different concentrations. Target Compound 1,1,1 Trichloroethane 2 Propanol Freon 113 Butanol 2-Methyl-2Propanol Ethyl Acetate Methanol m/pXylene O-xylene Propanone Calibrant (picanolone)

% RSD Part 1(n=18) % RSD Part 2 (n=18) 1/ko GC RT 1/ko GC RT 0.16 0.11 0.13 0.47 0.50 0.08 0.68 0.15 0.33 0.11 0.19 0.06 0.43 0.10 0.14 0.34 0.09 0.49 0.33 0.39 0.80 0.10 0.54 0.12 0.13 0.41 0.05 0.37 0.08 0.51 0.10 0.40 0.21 0.10 0.39 0.20

ITarget Compound I

I 2Butanone Ethanol Isoprene Benzene Toluene Calibrant Dichloromethane hexane Halon 1301 Ethanal 1 Freon 12/22

% RSD Part 1(n=18)

I GC RT 0.32 0.32 0.47

1/ko 0.84 0.10 0.08

0.15 0.17 0.80

0.41 0.10 0.56

0.44

0.20

0.43

0.16

% RSD Part 2 (n=18) GC RT 1/ko 0.10 0.38 0.48 0.09 0.65 0.06 0.23 0.11 0.42 0.12 0.26 0.07 0.41 1.31 0.37 0.32

0.06 1.54 0.08 0.16

The data shows the stability of the VOA instrument for these important identification parameters. As an example, the GC retention time is 890 seconds for 2- propanol and the 1/k o is 0.561. Therefore, the identification window would be set no smaller than three standard deviations: 890 ± 13 sec and 0.561 ± 85 of 130



February 2010

0.001; however in practice the windows are usually increased if the "analytical space" permits (2009 VOA database: 890±21 and 0.561±0.015 for 2-propanol).

After the VOA was calibrated in June 2001, the calibration was verified by challenging the VOA with a mixture that mimicked the ISS atmosphere. The contents of the mixture were unknown to the analyst operating the VOA. The detailed results are reported in reference [31.7.21], so only a summary will be providedhere. All samples volumes were 40 ml and a mass flow sensor controlled the sampling time to insure collection of 40 ml regardless of ambient pressure. Three consecutive runs of the challenge mixture were performed and the data reduced. Compounds in the mixture were properly identified in each run, which verified the identification capability of the VOA and the precision of the three runs met the precision requirement (+/-20%) for all compounds. The accuracy requirement was met for all but hexane (97%) and only two other compounds (ethanol and n-butanol) were greater than 30% error. In light of the excellent performance for all other compounds, the hexane was considered an anomaly and the VOA was shipped to KSC for launch. The VOA/RME, the first VOCs monitor, was prepared for flight in similar manner to the process outlined for the VOA. The VOA/RME successfully collected data throughout the STS-89 mission. [31.7.22] Two important design issues were recognized after looking at the data and comparing results to GSCs taken simultaneously with the runs. First, the sample volume (100ml) was too large and this was reduced to 40 ml and 10 ml for all subsequent VOA and VOA/RME activities. Secondly, it was clear that there was significant carryover from one run to next; therefore, Graseby, designed new reverse flow valves to clean the preconcentrators following sample desorption. The reverse flow valves solved the carryover issue and they were incorporated into the VOA (and later the VOA/RME). A unique opportunity arose to use the VOA/RME in submarine trials [31.7.23 and 31.7.241, when a joint effort between the U.S. Navy, United Kingdom (U.K.) Navy, and NASA was instituted to assess archival sampler performance on UK submarines. This study comparedresults from VOA/RME runs to those of simultaneously acquired archival samples. The VOA/RME eventually participated in two trials on UK submarines ( Figure 31.7.13). The VOA/RME may be the only actual equipment ever to analysis air on orbit and under the sea. The results from the first trial led to improvements in the UK sampler design. Concentrations for a representative target compound from the trials, toluene are shown in the following figures. It can be seen in Figure 31.7.14 that the archival samplers produced erratic concentrations 86 of 130



February 2010

compared to the VOA/RME in trial 1, but in trial 2 an improved archival sampler showed close agreement with the VOA/RME (Figure 31.7.15).

000

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— — — —

40

0

00

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Figure 31.7.13 VOA/RME

Figure 31.7.14: Trial 1: Toluene

000 +a

000

200

400

000

000

+000

U.— w/

Figure 31.7.15 Trial 2 Toluene

onboard submarine

The VOA was sent to ISS in August 2001 and activated in September 2001. A software issue between the VOA and the ISS 1553 communications bus led to intermittent operations for the first 6 months. The software issue significantly increased an already long validation time, consequently the first important use of the VOA occurred before it was formally validate. In February 2002, the ISS crew was preparing for an Extravehicular Activity (EVA) by regenerating METOX canisters (scrubbers for recycled air on EVAs). These canisters are a combination of charcoal and CO Z absorbent that are renewed by baking the sorbents and sending the effluent into the ISS volume. Normally, only metabolic contaminants from a crewmember are collected on the sorbents during the 8-10 hrs of an EVA and this can be released into the volume of ISS without a degradation in air quality. However, in February the crew was driven to seek shelter in the Service Module because of strong odors not long after the METOX regeneration had started. These canisters had been used many times before without incident. Possible causes included degraded Metox catalyst beds and crew error that caused cabin air to flow through the Metox sorbent for six months. If the latter cause were true, then the odors would have been caused by the release of ISS contaminants collected on the METOX sorbents over a 6-month period. The METOX canisters were regenerated again in April 2002 and although GSC samples would be acquired, they would not be analyzed before the ISS program had to decide whether to send up new 87 of 130


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canisters. Fortunately the VOA was available during the METOX regeneration and the two-part analysis allowed samples to be collected a couple hours apart. The results are summarized in Table 31.7.4, in which T = 0 is when the METOX regeneration was started and T = 2.5 hrs is the time predicted for the maximum contaminant release from the METOX regeneration. [31.7.25] The data indicate only a small rise in nominal contaminants supporting the view that a crew error and not sorbent degradation caused the large contaminant release in February 2002. The ISS program needed information to make a decision about whether to fly METOX canisters on the next Shuttle mission in a few weeks. The VOA was not yet validated for operations (see 31.7.26 for validation results), so ancillary data had to be collected to support the veracity of the VOA data collected during the METOX regeneration. First, GSCs collected in January 2002 and the latter part of 2001 were compared to the METOX data and it was found that the April data was representative of a nominal ISS atmosphere. Additionally, VOA sensor data confirmed that a 40 ml sample was acquired and that the preconcentrator and GC (flow and temperature profiles) performed nominally. Finally, a verification was required that compounds were correctly identified and quantified and this was done by comparing a ground calibration run (June 2001) to the data collected for two compounds in April 2002. The first compound was the late eluting compound, toluene, shown in Figure 31.7.16a. The GC retention times of all three runs are very Table 31.7.4: VOA data collected during the METOX incident in April 2002 PiA-1'. Pail" 2 . Pit. 1' Part'2 r Met^ aletmi erie. O-xylenez, ttiliiette

tier¢ene r nMrexane ca librant i6chlororrieth3ne

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X X.

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X X NA. 0.083

T.ower.` 'detecti

—0-I" X: 0 minute. X trace 123 :133 -4^ 0.102. • X-

:ti07

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close ( 1.5

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14:13

0.2

-0.5 1

- --^

10 46 o

2100 2150 2200 2250 2300 2350 2400 2450

VOA_8_04 GSC _

GC Retention time (s)

Figure 31.7.18 — Positive mode dilute runs

VOA_LA8_1 OSC_SM VOA_l _2 VOA_9_25 _18 q

Sample Date, Type, and Location

Figure 31.7.19 — Trending of contaminants

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Instrument Configuration-microAnalyzerTM In 2005, Sionex released a research-configured gas chromatograph/differential mobility spectrometer (GC/DMS), called the suitcase, which was used to compare performance of this new technology to the VOA. [31.7.28 and 31.7.29] The assessment of the suitcase model confirmed that VOCs could be desorbed from sorbent materials and sent through a GC column using air as a carrier gas. This was a significant breakthrough in the development of a small VOCs monitor because it eliminated the need for high-pressure gas cylinders or an interface with spacecraft gas supplies. Furthermore, the suitcase performance was impressive in measuring the low-molecular-weight polar compounds, which are many of the important analytes detected in spacecraft air. Two years ago Sionex began production of the first microAnalyzerSTM, which combined an inlet preconcentrator and a GC column interfaced to the DMS detector in an extremely small package. [31.7.30] The data presented in this section was collected using the microAnalyzerTM (Figure 31.7.20). The only additional peripherals for the MicroAnalyzer TM are a power supply and a laptop computer. A block diagram of the microAnalyzer TM is shown in Figure 31.7.21. A pump pulls an air sample through a small preconcentrator (Carbotrap B and Carboxen 1000), which removes the volatile organics from the air. The preconcentrator is heated to 300°C to desorb and transfer the VOCs to the head of the GC column (Varian VF-624MS 15m x 0.25 mm x 1.4 um). The GC column separates the complex mixture into its components and presents them to the detector.

. ample Pum

Pre- Concentrator

^ ^

Recircula tion I I Igorithm —I

Front End-Collection &

Separation

Figure 31.7.20 — microAnalyzer

GC

Detection

Scrubs

air

Figure 31.7.21 — microAnalyzerTM block diagram

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The detector measures two important parameters for each analyte: the GC retention time and the compensation voltage (V J. The peak area of the GC trace at a specific Vc is used to quantify the analyte concentration. The analyte ionization is identical to that described for the VOA, but the detection mechanism for the DMS, shown in Figure 31.7.22 is quite different. An RF voltage is combined with a set

Ve

Compensation Voltage (-5.OV) E:cc^rometer

Bottom Electrode I I

E'ectn,meter

Figure 31.7.22 — Ionization and separation mechanism The detector is composed of two closely-spaced electrodes through which the gas flow (GC column and make-up streams) moves the analyte ions from the ionization region to the electrometer, where they are detected. A radio frequency (RF) field, applied across the electrodes, is an asymmetric square wave with high and low field components cycling at 1.2 megahertz. The effect of these RF fields on the ions separates them in the vertical axis (direction of arrow labeled RF), as the gas flow pushes the ions toward the detector. The RF fields will push most ions to the walls before they reach the detector, unless a coupled voltage (compensation voltage V,) is applied. Selection of the proper RF voltage and V, for a compound will permit its ion to reach the detector, while other ions (formed in the ionization region) are driven to the walls. This provides the selectivity for ion detection even when several components elute from the GC column simultaneously. Greater detail on the detector can be found elsewhere. [31.7.31 and 31.7.32]

Calibration and Results-microAnalyzerTM The microAnalyzerTM was prepared for an experiment on ISS: a Station Detailed Test Objective (SDTO). Preparation was very similar to that described for the VOA, although the target list (Table 31.7.6) was reduced, because this was an experiment rather than operational hardware. [31.7.33] As with the VOA, the microAnalyzerTM starts calibration by establishing identification windows using GC

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times as one parameter, but the other dimensional parameter is the compensation voltage (Figure

31.7.23). Table 31.7.6 — microAnalyzerTM SDTO target list Acetaldehyde Methanol Ethanol Acetone Isopropanol 1-Butanol Ethyl Acetate

V,= 0.20

Dichloromethane Toluene Xylenes (o,m,p) 2-Butanone hexane Benzene Octamethylcyclotetrasiloxane

V,= -1.57

07

a

o

T

L Y 06

c

R

a. 0.5

04

I

1

0

1

100

200GC Window

300 GC Window

GC Time (sec)

Figure 31.7.23 — Peak windows for n-butanol and m/p Xyenes An independent unknown mixture, which included —I% carbon dioxide and 40% RH, was used to verify the instrument calibration and function. The automated results of the unknown challenge mixture showed 100% accurate identification of the components and 73% of the compounds accurately quantified (± 40%). Manual integration of two closely eluting compounds (methanol and acetaldehyde) produced an accuracy level greater than the 80% requirement. These results, along with the excellent precision of the data demonstrated the microAnalyzerTM was ready for the SDTO experiment.

The microAnalyzerTM has the capability to display results within a few seconds of the analysis completion; however, because the microAnalyzer was an experiment the crew did not have access to this information. The first step in the assessment of the microAnalyzerTM experiment was to evaluate the precision of the peak parameters used to identify the target compounds. Representative GC traces (long runs) over the microAnalyzer's operational period are shown in Figure 31.7.24. Representative 10s Runs-2009

0.95

J-17_10s2

0.9 —

—J,n24 10,2

Q

—Jue_tos2

t

_ 0.85 L

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Au910_10.2

O.6 -

01 y 0.75 Y CL

May19_10,2

— —May27_10.2

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C

00 C

O

N ^ C N C

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y

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<

0.6

^.

Ol

F

0.55

60

110

160

210

260

GC Retention Time (sec)

310

February 2010



Figure 31.7.24 — microAnalyzer GC run reproducibility May-September Excellent GC peak precision, together with the stable V, , meant accurate compound identification. The concentration of most compounds remains relatively constant in nominal conditions and that was the pattern observed. This confirms that the microAnalyzer TM has been working nominally and producing excellent results, but how accurate are the results? Data samples through July for ethanol and acetone concentrations from GSCs, microAnalyzer TM, and VOA are shown in Figures 31.7.25 and 31.7.26, with the GSC error bars set at ± 40%. The first two GSCs were acquired during microAnalyzerTM runs, but the last one (July 22) was sampled days away from the microAnalyzer runs due to operational issues. The microAnalyzer accuracy was generally good when compared to the GSCs. [31.7.34]

The microAnalyzer was operating during the hatch opening of the MPLM (Multi Purpose Logistics Module-supply vehicle) on September 1, 2009 and the results have boosted confidence in the instrument's capability. This event provided an opportunity to assess the microAnalyzerTM

•. 5.0

.nm(mrmo)440 (10 percent valley) as evidence by the doublet at mass 16 shown in Fig. 31.12.1. The peaks shown are from 160 and CH4, which have a mass difference of 1 part in 440. Resolution of the low mass channel was adequate to produce a valley of less than 1 percent between peaks at 15 and 16 Da.

Z v,

O

MASS (omu)

Figure 31.12.1 Mass doublet at 16 Da. Left peak is CH 4 at 16.0313 Da; right peak is O at 15.9949 Da. Valley between peaks is 9% of O peak height. The high bandwidth of the counter system, utilizing Be-Cu 16 stage discrete dynode electron multipliers, produced a dynamic range of over 6 decades. The CO 2 peak reached a counting rate of 9 MHz in flight. The background count accumulation was typically zero per integration period of 235 ms. Scanning of the mass spectrum occurred by stepping the ion acceleration high voltage to successive peak tops under the control of a microprocessor, an Intel 4-bit processor. A preset table of mass numbers including mass defects in the microprocessor defined the voltages for the selected mass numbers. The complete spectrum, consisting of 236 mass peak positions, was scanned at the rate of 4 samples per second in 59 s. A noble gas enrichment cell, the IRMC, was included in the instrument package to collect 107 of 130



February 2010

an atmospheric sample just after initiation of the instrument operation, purge the sample of CO2 and later (just before parachute jettison) introduce the sample into the mass spectrometer for measurement of the isotopic ratios of the enriched inert gases remaining in the cell.

Calibration of the flight instrument was performed using a high pressure, high temperature chamber, called the Venus Atmosphere Simulator, capable of reproducing the Venus descent profile of temperature and pressure down to the surface conditions (730 K and 90 Atm).

Bus Neutral Gas Mass Spectrometer The Pioneer Venus bus neutral gas mass spectrometer (BNMS) was designed to measure the number densities of neutral constituents in the Venus exosphere and thermosphere during its descent through the Venus upper atmosphere aboard the NASA Pioneer Venus multiprobe. [31.12.2] The BNMS sensor was a double-focusing magnetic deflection mass spectrometer. During the Venus entry the semi-open ion source was exposed directly to the influx of ambient constituents. Ionization of the neutral particles was achieved by a dual filament standard electron impact source using 56-eV electrons at an emission current of 100 microamps

Due to the bus entry velocity of 11 km/s the ambient particles of molecular mass M entered the ion source with a kinetic energy of about 0.69 M eV. Thus CO2 molecules approached the BNMS with a ram energy of 30 eV. Most particles were ionized after they had been thermalized in the ion source by reflections at the walls. Only a very small portion was ionized having their original ram energy. This energy difference could be used to differentiate between the thermalized and flythrough particles by operating the ion source in the normal and the so-called flythrough modes [31.12.3].

The magnetic analyzer (MA) consisted of an Alnico 700 magnet with a flux density of 0.5 T. and ion trajectory, R 1 , of 58.9 mm. Three collector slits covering the mass ranges 1-3, 4-8, and 12-46 Da. allowed simultaneous sampling of mass numbers 1 and 14; 2 and 28; 4 and 22; 8 and 44. The dynamic range of the ion counting collector system was extended via an electrometer amplifier connected to a grid in front of the spiraltron electron multiplier. There was a one order of magnitude overlap in the measurement ranges of the multiplier and electrometer. The principle mode of analyzer operation was peak stepping with a basic sampling time of 0.1 s per mass peak. The electrometer output signals were

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digitized into 10-bit words including 2 bits for range information. Operating power consumption was 4.6 W.

Bus Ion Mass Spectrometer and Orbiter Ion Mass Spectrometer Bennett radio frequency ion mass spectrometers on the Pioneer Venus Bus (BIMS) and Orbiter (OIMS) were identical. [31.12.4] The instrument design and operational characteristics were similar to those of ion spectrometers flown on previous missions, including those on the Atmosphere Explorer-C and -E spacecraft [31.11.2]. The analyzer orifice was oriented in the direction of spacecraft motion to ensure a relatively small angle of attack throughout the periapsis pass to eliminate spin modulation of the ion currents.

A unique feature incorporated in the BIMS and OIMS instruments was the explore/adapt logic sequence for regulating the consecutive measurements of individual ion species. This was accomplished in two steps: 1) periodic exploration of 16 preselected ion species, and 2) adaptive sequencing of repetitive ion measurements according to the relative significance of ion currents detected during the exploratory cycle. The explore/ adapt sequence thereby provides a spatial resolution of measurements inversely proportional to the number of ions encountered and thus automatically adjusts the measurement sequence so that information returned is optimized relative to the conditions encountered during the mission.

Orbiter Neutral Gas Mass Spectrometer The Pioneer Venus Orbiter mass spectrometer was a linear quadrupole instrument with a unique ion source that was enclosed, but exposed directly to the ambient atmosphere through a small aperture. [31.12.5] Anion repeller grid just inside the aperture was positively biased (approximately 40 V) to reject positive ions. Grids enclosing the ionization region were electrically biased so that all ions produced were drawn through a retarding grid into the quadrupole analyzer. The grid assembly functioned as a miniaturized retarding potential analyzer for analysis of direct streaming neutral particles.

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The ion source could be operated either as a closed source or open source. A weak angle of attack dependence, (a cosine function) made the closed source mode useful for measurements at large angles of attack. It also provided a sensitivity enhancement over the open mode.

In the open source mode, the potentials of the source grids allowed free streaming particles to enter the retarding field that discriminated between those with relatively large kinetic energy and those that were thermalized to the ion source region temperature. The ions produced from thermalized surface reflected particles were rejected while those with enough kinetic energy to overcome the retarding field were passed into the quadrupole mass analyzer. The sensitivity was determined by laboratory calibration using high velocity molecular beams and in flight by comparing measurements made of nonreactive species in both operating modes.

The ion source was covered by a metal-ceramic break-off cap that was removed by a pyrotechnic actuator after orbit insertion. The quadrupole mass filter consisted of hyperbolically contoured rods 7.5 cm long with a field radius of 0.2 cm. The secondary electron multiplier was a Be-Cu 14 dynode box and grid design.. The average power consumption of the instrument was 12 W. The weight of the instrument was 3.8 kg. The ion source had redundant filaments that could operate at either - 70 eV or 27 eV.

The mass peaks produced by the assembly had flat tops that permitted stepping from mass unit to unit without requiring peak searching. Three operational modes mass were programmed to scan individually any 8 selected mass numbers (0 to 46 Da), to scan sequentially 0 to 46 Da at unit increments (search mode) or to scan sequentially 0 to 46 Da at 1/8 Da increments (diagnostic mode). Ion counting was employed but at high signal levels where the counting system had a significant dead-time, the anode current at the multiplier was used as a measure of the ion current. The dynamic range of the instrument was greater than 106. 31.13 Mars Phoenix Mass Spectrometer

Major components of the Phoenix mass spectrometer were: 1) a gas handling manifold containing a gas transfer tube from the Thermal Analyzer (TA) ovens to the MS ion source, the TA gas inlet valve and microleak, an atmospheric gas inlet valve and microleak,; 2) the magnetic sector field mass with four 110 of 130



February 2010

electron multiplier detectors and associated electronics circuits; and 3) a small sputter-ion pump to maintain a good vacuum in the analyzer. [31.13.1 ]

The two inlet paths through the gas manifold admitted gases into the ion source of the instrument. These were (a) a direct path through the transfer tube from the Thermal Evolved Gas Analyzer (TEGA) furnace and (b) a direct path from the atmosphere through a short transfer tube that fed gas into the atmosphere inlet valve on the ion source. The entire manifold and transfer tubes were heated to 35 °C to keep water vapor and other volatiles from freezing onto the walls The microleaks that control the rate of gas flows into the MS ion source consisted of a bundle of capillary glass tubes drawn out to reduce their diameters so that the conductance of the bundle was about "5 1x10 cc/sec. for the TA inlet and somewhat larger for the atmosphere inlet. Gasses admitted to the ion source flowed out of it through the ion object slit (conductance 5 cc/sec.) into the mass analyzer vacuum chamber maintaining an equilibrium pressure of 8x10 -6 mbar. A sputter ion pump maintained an analyzer pressure of less than 1x10-7 mbar. The mass spectrometer ion source was a Nier type with redundant filaments. Two emission currents (25µA and 200µA) and four electron energies (90eV, 37eV, 27eV and 23eV) were controlled by a microprocessor. The magnetic analyzer had four channels that covered the mass ranges 0.7-4, 7-35, 1470 and 28-140 Da. The mass resolution for the highest mass range was set at 140 (M/AM). The mass resolution of the other channels was proportionally reduced. Ion counting detectors were employed. The maximum ion counting rate was 2 megahertz. The preamp frequency was 12 megahertz. The high sensitivity added a factor of 8, for a dynamic range of 1.6 x 107 . By summing the counting rates for 100 measurements, a gas at the 100 ppb mixing ratio'level (partial pressure of 1 x 10 "12 mbar) could be measured at a statistical precision of 10%; at 10 ppb (partial pressure of 1 x 10 -13 mbar) the precision is 30%. The realized sensitivity depended on the residual peak amplitude at the particular m/z of interest. The NeBFe magnet of had a field strength of 0.65T with a mass of only 500 grams. Mass was a critical parameter in the design of the instrument.

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Figure 31.13.1 Complete mass spectrometer package

Figure 31.13.1 shows the complete mass spectrometer package. The mass analyzer is at the top with the ion source at the right. The high vacuum valves protrude down ward from the ion source housing. The gas manifold lies across the bottom.

20; Figure 31.13.2 Picture of the TEGA electronics assembly. The electronics subsystem consists of three modules, the Processor Module, Low Voltage Module and High Voltage Module mounted on top of the instrument support plate as shown in Figure 31.13.2. The electronics were functionally similar to those of previously flown mass spectrometers. The processor 112 of 130



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module consisted of a dedicated 80C 196KD microprocessor, FPGA, memory, bus drivers and associated circuitry required to control and monitor the instrument functions as well as to store accumulated data.

The high voltage module provided the precision ion accelerating voltage (200 to 2000V) stepping power supply for the ion source that was controlled by a 16 bit D/A converter. For standard stepping, the precision of the output voltage was better than 14 bits after the 5 ms settling interval. The high voltage module also contained the filament emission circuitry plus electron multiplier and ion pump power supplies. For an instrument that is to operate on the surface of Mars, all high voltages must employ special electrostatic shields to prevent corona discharges in the 8 to 10 mb atmospheric pressure environment. Each high voltage module employed an encapsulated Faraday Shield to prevent high voltage breakdown. However, the emission control section used a special shielded enclosure without encapsulation. High voltage connections to the analyzer were also shielded using special vacuum feedthrus with shielded cables and boots that sealed each connector to its respective vacuum feedthru.

Two operating modes were available. One, the sweep mode, consisted of sweeping the ion accelerating voltage across the entire mass range over the 4 channels to provide a broad brush look at the composition of the gas sample. The other mode, the hops mode, involved hopping from peak top to peak top. On a given peak, 7 measurements of counting rate were made while stepping over the top of the peak. The amplitude of the peak was determined by fitting a curve to the 7 data points. The mass spectrometer mass was 5.7 kg, power was ..13 watts, and volume was 24x23x18 cm.

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Ch 31 - MS in Space

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31.14 Reference Information

31.1.1 Aerojet Aerobee Rocket, Fact Sheets of the National Museum of the US Air Force, Web Site. 31.1.2 Radiofrequency Mass Spectrometer, Bennett, W. H., J. Applied Phys. 21, 143-149, 1950. 31.1.3 Small General Purpose Double-Focusing Mass Spectrometer, Nier, A. O., Rev. Sci. Instr., 31 2217-1132, 1960. 31.1.4 Neutral Composition of the Atmosphere in the 100 - 200 Kilometer Range, Nier, A. O., J. H. Hoffman, C. Y. Johnson and J. C. Holmes, J. Geophys. Res., 69, No. 5, 979-989. 1064. 31.1.5 Neutral Constituents of the Upper Atmosphere: Minor Peaks observed in a Mass Spectrometer, Nier, A. O., J. H. Hoffman, C. Y. Johnson and J. C. Holmes, J. Geophys. Res., 69, No. 21, 4629-4636, 1064. 31.1.6 Ion Mass Spectrometer on Explorer XXXI Satellite, Hoffman. J. H. Proceedings of the IEEE 57, No. 6, 1063-1067, 1969. 31.1.7 Daytime Midlatitude Ion Composition Measurements, Hoffman, J. H., C. Y. Johnson, Holmes, J. C. and Young, J. M., J. Geophys. Res., 74, No. 26, 6281-6290,1969 31.1.8 Ion Concentrations and fluxes in the Polar Regions During Magnetically Quiet Times, Hoffman, J. H. and W. H. Dodson, J. Geophys. Res. 85, No A2, 626-632,1980. 31.1.9 A Mass Spectrometric Determination of the Composition of the Nighttime Topside Ionosphere Hoffman, J. H., J. Geophys. Res., 72, No. 7, 1883-1888, 1967. 31.1.10 Lunar Orbital Mass Spectrometer Experiment, Hoffman, J. H. Hodges, R. R. and Evans, D. E. , Proceedings of the Third Lunar Science Conference, Supplement 3, Geochimica et Cosmochimica Acta, 3, 2205-2216, 1972 31.1.11. Lunar Atmospheric Composition Results from Apollo 17, J. H. Hoffman, R. R. Hodges, Jr. F. S. Johnson and D. E. Evans, Proc. of the Fourth Lunar Science Conference, Supplement 4, Geochimica et Cosmochimica Acta, 3, 2865-2875, 1973. 31.1.12 The Lunar Atmosphere, Hodges, Jr., R. R., J. H. Hoffman, and F. S. Johnson, Icarus, 21, 415-426, 1974. 31.1.13 The Atmospheric Explorer Mission, Dalgarno, A, W. B. Hanson, N. W. Spenser, E. R. Schmerling, Radio Science, 8, No. 4. 263-266, 1973. 31.1.14 An encounter with Venus, Colon, L., Science, 203, 23 February, 743-744, 1979. 114 of 130



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31.1.15 Venera Mass Spectrometer experiment, Istomin, V. G. , K. V. Grechnev, V. K. Kochnev, V. A. Pavlenko, L. N. Ozerov, andv. G. Klimovitsky,h. 5, 4, 1979. 31.1.16 Composition and Structure of the Venus Atmosphere, Hoffman, J. H., R. R. Hodges, M. B. McElroy, T. M. Donahue, M. Koplin, Science, 205, 6, July, 49-51, 1979. 31.1.17 Venus Was Wet: A Measurement of the Ratin of Deuterium to Hydrogen, Donahue, T. M., J. H. hoffman, R. R. Hodges, Jr., and A. J. Watson, Science, 216, 7 May 1082, 630-633. 31.1.8 Measurements of the Venus Lower Atmosphere Composition: A comparison of Results, Hoffman, J. H., V. I. Oyama, U. von Zahn, J. Geophys. Res. 85, No. A 13, 7871-7881 1980. 31.1.19 Venus Upper Atmosphere Neutral Composition, Niemann, H. B., R. E. Hartle, W. T. Kasprzak, N. W. Spenser, S. H. Way, D. M. Hunten, and G. R. Carignan, Science, 203, 23 February, 770-772, 1979. 31.1.20 In Situ Gas and Ion Measurements at Comet Halley, Krankowsky, D, P. Lammerzahl, L. Herrwerth, J. Woweries, P. Eberhardt, U. Dolder, U. Herrmann, W. Schulte, J. J. Berthelier, J. H. Illiano, R. R. hodges and J. H. Hoffman, Nature, 321, No 6067, 326-329, 1986. 31.1.21 An overview of the descent and landing of the Huygens probe on Titan Lebreton, Jean-Pierre; Witasse, Olivier; Sollazzo, Claudio; Blancquaert, Thierry; Couzin, Patrice; Schipper, Anne-Marie; Jones, Jeremy B.; Matson, Dennis L.; Gurvits, Leonid I.; Atkinson, David H.; Kazeminejad, Bobby; Perez-Ayucar, Miguel. Nature, 438,. 758-764. 2005. 31.1.22 The abundances of constituents of Titan's atmosphere from the GCMS instrument on the Huygens probe, H. B. Niemann, S. K. Atreya, S. J. Bauer, G. R. Carignan, J. E. Demick, R. L. Frost, D. Gautier, J. A. Haberman, D. N. Harpold, D. M. Hunten, G. Israel, J. I. Lunine, W. T. Kasprzak, T. C. Owen, M. Paulkovich, F. Raulin, E. Raaen, S. H. Way, Nature 438: 779-784 2005. 31.1.23 Composition and Structure of the Martian Atmosphere: Preliminary Results from Viking 1 Nier, A. O, W. B. Hanson, A. Sieff, M. B. McElroy, N. W. Spenser, R. J. Duckett, T. C. D. Knight, and W. S. Cook, Science 27 August 1976: 786-788. 31.1.24 Composition of the Atmosphere at the Surface of Mars: Detection of Argon-36 and Preliminary Analysis, Owen, T and K. Biemann, Science 27 August 1976: 801-803.

31.1.25 Water at the Phoenix Landig Site, P.H. Smith, L.K. Tamppari, R.E. Arvidson, D. Bass, D. Blaney, W.V. Boynton, A. Carswell, D.C. Catling, B.C. Clark, T. Duck, E. DeJong, D. Fisher, W. Goetz, H.P. Gunnlaugsson, M.H. Hecht, V. Hipkin, J. Hoffman, S.F. Hviid, H.U. Keller, S.P. Kounaves, C.F. Lange, M. Lemmon, M.B. Madsen, M. Malin, W.J. Markiewicz, J. Marshall, C.P. McKay, M.T. Mellon, D.W. Ming, R.V. Morris, N. Renno, W.T. Pike, U. Staufe, C. Stoker, P. Taylor, J. Whiteway, A.P. Zent, Science, 3 July, 58-61, 2009. 115 of 130



February 2010

31.1.26 Evidence for Calcium Carbonate at the Mars Phoenix Landing Site, Boynton, W. V., W. Ming, S. P. Kounaves, S. M. M. Young, R. E. Arvidson, M. H. Hecht, J Hoffman, P. B. Niles, D. K. Hamara, R. C. Quinn, P. H. Smith, B. Sutter, D. C. Catling, R. V. Morris, Science, 3 July, 61-64, 2009.

31.1.2.1 Johnston, R.S. and Dietlein, L. (ed), Biomedical Results of Skylab, NASA SP377, NASA Scientific and Technical Information Office, Washington, D.C., 1977., Chapter 36. 31.1.2.2 Michel, E.L., Rummel, J.A., and Sawin, C.F. "Skylab experiment M-171 `Metabolic Activity'results of the first manned mission", Acta Astronautic Vo12, 1975, pp. 351-365. 31.1.2.3 Johnston, R.S., Dietlein, L.F., and Berry, C.A. (ed), Biomedical Results of Apollo, NASA SP368, NASA Scientific and Technical Information Office, Washington, D.C., 1975, Section II, Chapter 7. 31.1.2.4 Perry, C.L., "Metabolic Analyzer", NASA Technical Memorandum TM X-64797, June 1971. Pp 1-2. 31.1.2.5 op. cit. Michel p. 353. 31.1.2.6 Lehotsky, R., "A Mass Spectrometer Sensor System for Metabolic Analysis and Atmospheric Monitoring on Skylab and Future Manned Spacecraft", Proceedings of the 21 s' Annual Conference on Mass Spectrometry and Allied Topics, San Francisco, CA., May 20-25, 1973, pp 403-411. 31.1.2.7 "Life Sciences Flight Experiment Program: Life Sciences Laboratory Equipment (LSLE) Descriptions", Document # JSC-16254-G, May 1984. pp. 18-21. 31.1.2.8 http://Isda.isc.nasa.gov/scripts/hardware/hardw.cfm?hardware id=175 31.1.2.9 Samonski jr., F.H., "Technical History of the Environmental Control for Project Mercury", NASA Technical Note TN D-4126, October 1967. 31.1.2. 10 "Flammability, Odor, Offgassing, and Compatibility Requirements and Test Procedures for Materials in Environments that Support Combustion", NASA: NHB 8060.1 C (latest version), April 1991. 31.1.2.11 Nelson, N. (Chairman, Panel on Air Standards for Manned Space Flight), "Atmospheric Contaminants in Spacecraft", National Academy of Sciences, 1968.

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31.1.2.12 Wands, R.C. (Director, Advisory Center on Toxicology), "The Relationship of NASA Occupational Medicine and Environmental Health with the Advisory Center of Toxicology, National Research Council, NAS, October 1969. 31.1.2.13 "Spacecraft maximum Allowable Concentrations for Airborne Contaminants", NASA document: JSC 20584 (latest version). 31.1.2.14 "Guidelines for Developing Spacecraft Maximum Allowable Concentrations for Space Station Contaminants", National Academy Press, Washington, D.C., 1996. 31.1.2.15 "Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants", Volume 1, National Academy Press, Washington, D.C., 1994. 31.1.2.16"Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants", Volume 2, National Academy Press, Washington, D.C., 1996. 31.1.2.17 "Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants", Volume 3, National Academy Press, Washington, D.C., 1996. 31.1.2.18 "Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants", Volume 4, National Academy Press, Washington, D.C., 2000. 31.1.2.19 "Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants", Volume 5, National Academy Press, Washington, D.C., 2008. 31.1.2.20 op. cit. Samonski, jr. 31.1.2.21 op. cit. Johnson, R.S., Biomedical Results of Apollo 31.1.2.22 Gohlke, R.S. and McLafferty, F.W., "Early Gas Chromatography/Mass Spectrometry", J. Am. Soc. Mass Spectrom.,

1993, 4, 367-371.

31.1.2.23 Parker, jr., J.F., West, V. (editors) Bioastronautics Data Book, NASA-3006, 2nd edition, 1973. 31.1.2.24 "The Proceedings of the Skylab Life Sciences Symposium, Volume 1", Lyndon B. Johnson Space Center, August 1974, JSC-09275 or NASA Technical Memorandum TM X-58154, November 1974. 31.1.2.25 Liebich, H., Bertsch, W., Zlatkis, A., Schneider, H., "Volatile Organic Components in the Skylab 4 Spacecraft Atmosphere," Aviation, Space, and Environmental Medicine, August 1975, pp. 1002-1006. 31.1.2.26 Galen, T.J., Solid Sorbent Air Sampler United States patent #4584887, 1986.

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31.1.2.27 Limero, T., "Solid Sorbent Air Sampler for the Characterization of Contaminants in Spacecraft Atmospheres", Proceedings of 1990 EPA/AW&MA International Symposium: Measurement of Toxic and Related Air Pollutants, Raleigh, N.C., 1990. 31.1.2.28 EPA Air Toxic Monitoring methods (TO-14a and TO-15) http://www.epa.gov/ttnaintiI/airtox.htmi 31.1.2.29 ibid, EPA Air Toxic Monitoring methods (TO-1, TO-14a, TO-15, and TO-17) 31.1.2.30 Palmer, P.T., Wong, C.M., "Development of Ion Trap Mass Spectrometric Methods to Monitor Air Quality for Life Support Applicationsm," 23 `d International Conference on Environmental Systems, Technical Paper # 932206, Colorado Springs, CO., July 1993. 31.1.2.31 Palmer, P.T. and Limero, T.F., Mass Spectrometry in Space. 31.1.2.32 Wyatt, J., http://www.navy.mil/navvdata/cno/n87/usw/issue_10/breathe.html. 31.1.2.33 Daley, T., "Keynote Address: The Evolution of Submarine Air Monitoring and Air Purification in the US Navy", Submarine Air Monitoring and Air Purification (SAMAP) conference proceedings, Amsterdam, NE, 2005. 31.1.2.34 Steiner, G, Edeen, M., and Ransom, E., "On Orbit Performance of the Major Constituent Analyzer" 32 nd International Conference on Environmental Systems, Technical Paper 2002-012404, San Antonio, TX., 2002. 31.1.2.35 ibid Steiner 31.1.2.36 Eiceman, G.A., et.al ., "Ion Mobility Spectrometry of Hydrazine, Monomethylhydrazine, and Ammonia in Air with 5-Nonanone Reagent Gas, Anal. Chem., 1993, 65, pp 1696-1702. 31.1.2.37 Limero, T.F., et.al ., "A Volatile Organic Analyzer for Space Station: Description and Evaluation of a Gas Chromatography/ Ion Mobility Spectrometer", 22 nd International Conference on Environmental Systems, Technical Paper 921385, Seattle, WA., 1992. 31.1.2.38 Searching for Life On Mars: The Development of the Viking Gas Chromatograph Mass Spectrometer (GC/MS)http://www.nasa.gov/pdf/384151iiiain Viking GCMS_case _studypdf 31.1.2.39 Brittain, A., Bass, P., Breach, J., and Limero, T., "Instrumentation for Analyzing Volatile Organic Compounds in Inhabited Enclosed Environments", 30"' International Conference on Environmental Systems, Technical Paper 2000-01-2434, Toulouse, FR., 2000. 31.1.2.40 Limero, T., Reese, E., Trowbridge, J., Hohman, R., .Tames, J.T., "The Volatile Organic Analyzer (VOA) Aboard the International Space Station", b

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31.1.2.41 Limero, T., "Revalidation of the Volatile Organic Analyzer Following a Major On Orbit Maintenance Activity," 37th International Conference on Environmental Systems, Technical Paper 2007-01-3220, Chicago, IL., 2007. 31.1.2.42 Limero, T. and Reese, E., "First Operational Use of the ISS-VOA in A Potential Contingency Event", International Journal for Ion Mobility Spectrometry, 5(2002)3, pp. 27-30. 31.1.2.43 Limero, T., "Volatile Organic Analyzer (VOA) in 2006: Repair, Revalidation, and Restart of Elektron Event", International Society for Ion Mobility Spectrometry (ISIMS) Conference Proceedings, 2007. 31.1.2.44 Limero, T., Cheng, P., and Boyd, J., "Evaluation of Gas Chromatography-Differential Mobility Spectrometry for Measurement of Air Contaminants in Spacecraft", 36th International Conference on Environmental Systems, Technical Paper 2006-01-2153, Norfolk, VA., 2006. 31.1.2.45 http://www.sionex.com/products/downloads/SIONEX-Introduces-the-microAnalyzer.pdf 31.1.2.46 Chutjian, A., et.al, "Overview of the Vehicle Cabin Atmosphere Monitor, a Miniature Gas Chromatography/Mass Spectrometer for Trace Contaminant Monitoring on the ISS and CEV," 37th International Conference on Environmental Systems, Technical Paper 2007-01-3150, Chicago, IL., 2007. 31.1.2.47 Chutjian, A., Darrach, M., Bornstein, B., Croonquist, A., and Edgu-Fry, E., "Results from the Vehicle Cabin Atmosphere Monitor: A Miniature Gas Chromatograph/Mass Spectrometer for Trace Contamination Monitoring on the ISS and Orion," 38 th International Conference on Environmental Systems, Technical Paper 2008-01-2045, San Francisco, CA., 2008.

31.1.4.1)

Goodrich, W. D., "Viscous flow effects on hydrogen leaks from cracks in the Orbiter Challenger main engines", American Institute of Aeronautics and Astronautics, Aerospace Sciences Meeting, 22nd, Reno, NV, Jan. 9-12, 1984.

31.1.4.2)

Seymour, "STS-35 Scrub 3 Hydrogen Leak Analysis", NASA Technical Memorandum TM-103548, July 1991.

31.1.4.3)

"Hydrogen Leak Discovered on Shuttle Atlantis", NASA Press Release 90-89, 29 June 1990.

31.1.4.4)

"STS-73/Columbia Launch Scrub", KSC Shuttle Status, 28 September 1995. 119 of 130


31.1.4.5)


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"STS-93 Mission Archive", http: //www. nasa. gov/mission_pages/shuttle/shuttlemissions/archives/sts-93 .html.

31.1.4.6)

Harwood, W., "Oxygen leak delays shuttle Endeavour's launch", Spaceflight Now, 11 November 2002, http://spaceflightnow.com/station/stageI Ia/021I IOscrub/.

31.1.4.7)

"NASA Shuttle Launch Targeted for No Earlier Than March 15", NASA Press Release 09059, 11 March 2009.

31.1.4.8)

"NASA Postpones Launch of Space Shuttle Endeavour", NASA Press Release 09-135, 13 June 2009.

31.1.4.9)

"Fuel Leak Again Postpones Launch of Space Shuttle Endeavour", NASA Press Release 09-138, 17 June 2009.

31.1.4.10) Helms, W. R.; Raby, B.A., "A Prototype Hazardous Gas Detection system for NASA's Space Shuttle" , 26 `h ASMS Conference on Mass Spectrometry and Allied Topics, St. Louis, MO, 1978, 463-465. 31.1.4.11) Helms, W. R. "History, Design, and Performance of the Space Shuttle Hazardous Gas Detection System," Space Shuttle Technical Conference, Houston, TX, June, 1983, NASA Conference Publication 2342, Part 1, 573-580. 31.1.4.12) Bill Helms, personal communication. 31.1.4.13) Wyatt, J.R., "Development of a Small Magnetic Mass Spectrometer for Atmosphere Analysis/Process Control", Int. J. Mass Spec. Ion Process, 1984, 60, 289-297. 31.1.4.14) Griffin, T. P.; Breznik, G. S.; Mizell, C. A.; Helms, W. R.; Naylor, G. R.; Haskell, W. D. "A Fully Redundant On-Line Mass Spectrometer System Used To Monitor Cryogenic Fuel Leaks on the Space Shuttle" Trends Anal. Chem., 2002, 21(8), 488-497.

31.2.1)

"Introduction to Helium Mass Spectrometer Leak Detection", Varian Vacuum; 2nd edition (1995).

31.2.2)

Orvis M. Knarr, "Industrial Gaseous Leak Detection Manual" McGraw-Hill Professional Publishing (December 1, 1997)

31.2.3)

Luke Hinkle, "If they don't control Mass Flow, Why Do We call Them `Mass Flow Controllers?"', Vac. Tech and Coating (Sept, 2007) GD&D, pp 4-6. 120 of 130



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31.3.1) Griffin, T. P.; Breznik, G. S.; Mizell, C. A.; Helms, W. R.; Naylor, G. R.; Haskell, W. D. "A Fully Redundant On-Line Mass Spectrometer System Used To Monitor Cryogenic Fuel Leaks on the Space Shuttle" Trends Anal. Chem., 2002, 21(8), 488-497. 31.3.2)

Dawson, P. H. Quadrupole Mass Spectrometry and its Applications. Elsevier: Amsterdam, 1976.

31.3.3) G. C. Rhoderick, W. J. Thorn, W. R. Miller, F. R. Guenther, E. J. Gore and T. O. Fish, "Gas Standards Development in Support of NASA's Sensor Calibration Program around the Space Shuttle" Anal. Chem., 2009, 81 (10), 3809-3815. 31.3.4)

STS-113, Personal Communications with Hazardous Gas Detection Launch Team, 2002.

31.5.1) Johnston, R.S., Dietlein, L.F., and Berry, C.A. (ed), Biomedical Results of Apollo, NASA SP-368, NASA Scientific and Technical Information Office, Washington, D.C., 1975, Section II, Chapter 7. 31.5.2)

Cardus, D. "Effects of 10 days recumbency on the response to the bicycle ergometer test", Aerospace Med., 37:993-999, 1966.

.31.5.3)

Hyatt, K.H., Kamenetsky, L.G., and Smith, W. M., "Extravascular dehydration as an etiologic factor in post-recumbency orthostatism", Aerospace Med., 40: 644-650, 1969.

31.5.4)

Miller, P.B., Johnson, R.L., and Lamb, L.E. "Effects of moderate physical exercise during four weeks of bed rest on circulatory functions in man", Aerospace Med., 36:1077-1082, 1965.

31.5.5) Saltin, B., Blomquist, G., Mitchell, J.H., Johnson Jr, R. L„ Wildenthal, K., and Champman, C.B., "Response to exercise after bed rest and after training. A longitudinal study of adaptive changes in oxygen transport and body composition", Circulation, 38:178, 1968. 31.5.6)

op. cit. Johnston, Biomedical Results of Apollo Section lII.

31.5.7)

Johnston, R.S., and Dietlein, L.F(ed), Biomedical Results of Skylab, NASA SP377, NASA Scientific and Technical Information Office, Washington, D.C., 1977.

31.5.8)

Ibid, Johnston, Biomedical Results of Skylab, Chapter 36. 121 of 130


31.5.9)


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Sawin, C.F., Taylor, G.R., and Smith, W., Extended Duration Orbiter Medical Project: Final Report 1989-1995, NASA/SP-1999-534, 1999.

31.5.10)

ibid, Sawin, Section 3.

31.5.11)

"Life Sciences Flight Experiment Program: Life Sciences Laboratory Equipment (LSLE) Descriptions", Document # JSC-16254-G, May 1984. pp. 18-21.

31.5.12)

Personal communications (Statement of Work for Gas Analyzer System for Metabolic Analysis Physiology).

31.5.13)

West, J., Human Experiments on Spacelab SLS-1, Pubmed.gov , Volume 34, Issue 1, 1991.

31.5.14)

Huff, W. Spacelab Life Sciences-2, PubMed.gov , Voll, Issue 1, 1994, pp.3-1.

31.5.15)

Cooke, W.H., et.al ., "Nine Months in space: effects on human autonomic cardiovascular regulation", J. Appl Physiol, Vol 89, 2000, pp. 1039-1045.

31.5.16)

http://www.nasa.gov/centers/marshall/pdf/115941main hrf.pd£

31.5.17)

http://Isda.jsc.nasa.^pts/hardware/hardconfig.cfm?hardware ov index = 1601&exp inde X=O.

31.5.18)

Personal communications: William Niu (Hamilton-Sunstrand).

31.5.19)

"Life Sciences Flight Experiment Program: Life Sciences Laboratory Equipment (LSLE) Descriptions", Document # JSC-16254-G, May 1984. pp. 18-21.

31.5.20) Lehotsky, R., "A Mass Spectrometer Sensor System for Metabolic Analysis and Atmospheric Monitoring on Skylab and Future Manned Spacecraft", Proceedings of the 21" Annual Conference on Mass Spectrometry and Allied Topics, San Francisco, CA., May

20-25, 1973, pp 403-411. 31.5.21)

Michel, E.L., Rummel, J.A., and Sawin, C.F. "Skylab experiment M-171 `Metabolic Activity'-results of the first manned mission", Acta Astronautic Vo12, 1975, pp. 351-365.

31.5.22)

Personal communications: Presentation (GAMS SLS-1 Anomalies) to SLS-1 Payload Oversight Committee.

31.5.23)

http://Isda.isc.nasa. ov/scripts/hardware/hardw.cfm?hardware_id=175.

31.5.24)

http://wwwl.nasa.gov/centers/marshall/news/background/facts/hrf.html.

31.5.25)

http://Isda.isc.nasa.gov/scripts/experiment/exper.cfm?exp index=903.

31.5.26)

Robinson, J., Rhatigan, J., and Baumann, D, "International Space Station Research Summary Through Expedition 10", NASA/TP-2006-21346.

31.5.27)

http://www.nasa.gov/mission pages/station/science/experiments/PFS.html. 122 of 130


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Prisk, G., Elliott, A., and West, J., "Sustained microgravity reduces the human ventilator response to hypoxia but not to hypercapnia", J. Appl Physiol., 88:1421-1430, 2000.

31.5.29)

Prisk, G., Fine, J., Cooper, T., West, J., "Vital capacity, respiratory muscle strength, and pulmonary gas exchange during long-duration exposure to microgravity", J. Appl Physiol., 101:439-447, 2006.

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31.6.1)


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Flammability, Odor, Offgassing, and Compatibility Requirements and Test Procedures for Materials in Environments that Support Combustion", NASA: NHB 8060.1 C (latest version), April 1991.

31.6.2)

Spacecraft Maximum Allowable Concentrations for Airborne Contaminants", NASA document: JSC 20584 (latest version).

31.6.3)

Reuter, J., Reysa, R., "International Space Station Environmental Control and Life Support System Status: 2000-2001 ", 31" International Conference on Environmental Systems Technical Paper 2001-01-2386, Orlando, FL., 2001.

31.6.4)

EPA Air Toxic Monitoring methods ( TO-15r), http://www.epa.gov/ttanamtil/airtox.html

31.6.5)

Toxicology Laboratory ISO9001 Work Instruction

31.6.6)

EPA Air Toxic Monitoring methods (TO-14a and TO-15) http://www.epa.gov/ttnamtiI/airtox.htmI

31.6.7) Palmer, P. and Limero, T., "Mass spectrometry in U.S. space program: past, present, and future" Journal of the American Society of Mass Spectrometry, Volume 12, Issue 6, June 2001, pp. 656-675 31.6.8)

James, J., "A History of Space Toxicology Mishaps: Lessons Learned and Risk Management", 39`" International Conference on Environmental Systems, Technical Paper 2009-01-2591, Savannah, GA, 2009.

31.7.1)

Rotheram, M.A., "Atmospheric Composition Monitor Assembly for Space Station Freedom Environmental Control and Life Support System," SAE Technical Paper Series 891451, 19th Intersociety Conference on Environmental Systems, San Diego, CA., 1989

31.7.2)

Torres, D.A., Cole, A., and Hiss, J., "Stand Alone Major Constituents Analyzer Flight Design", SAE Technical Paper Series 94'50 , 24th International Conference on 3 Environmental Systems, Friedrichshafen, Germany, 1994

31.7.3)

Coleman, M. reference 124 of 130


31.7.4)


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Niu, W., Rotheram, M.A., Dencker, W., and Davidson, L. "The development of an Atmospheric Composition Monitor for the Environmental Control and Life Support System," SAE Technical Paper Series 921149, 22nd International Conference on Environmental Systems, Seattle, WA., 1992

31.7.5)

McHard, R., Reysa, R., Granaham, J., "Accuracy Assessment of the Major Constituent Analyzer", 35 th International Conference Environmental Systems, Technical Paper 200501-2893.

31.7.6)

Steiner, G., Edeen, M., Ransom, E., and Gentry, G., "On-Orbit Performance of the Major Constituent Analyzer", 32 nd International Conference on Environmental Systems, Technical Paper 2002-01-2404, San Antonio, TX., 2002.

31.7.7)

Gentry, G., Reysa, R., and Lewis, J., "International Space Station (ISS) Environmental Control and Life Support (ECLS) System Equipment Failures, Causes, and Solutions February 2001-February 2002", 32 nd International Conference on Environmental Systems, Technical Paper 2002-01-2495, San Antonio, TX., 2002.

31.7.8)

Reysa, R., Granaham, J., Steiner, G., Ransom, E., and Williams, D., "International Space Station (ISS) Major Constituent Analyzer (MCA) On-Orbit Performance", 34th International Conference on Environmental Systems, Technical Paper 2004-01-2546.

31.7.9)

Gentry, G., Reysa, R., and Williams, D., "International Space Station (ISS) Environmental Control and Life Support (ECLS) System Overview of Events: February 2002-2004, 34th International Conference on Environmental Systems, Technical Paper 2004-01-2383.

31.7.10)

Limero, T., Beck, S., and James, J., "Development and Performance of the Oxygen Sensor in the CSA-CP Aboard the International Space Station", 34 th International Conference on Environmental Systems, Technical Paper 2004-01-2337, Colorado Springs, CO., 2004

31.7.11)

Williams, D., Gentry, G., "International Space Station Environmental Control and Life Support System Status: 2003-2004", 34th International Conference on Environmental Systems, Technical Paper 2004-01-2382, , Colorado Springs, CO., 2004

31.7.12)

op. cit., Reysa

31.7.13)

"The Proceedings of the Skylab Life Sciences Symposium, Volume 1", Lyndon B. Johnson Space Center, August 1974, JSC-09275 or NASA Technical Memorandum TM X58154, November 1974.

125 of 130


31.7.14)


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Garcia, H., Limero, T., James, J., "Setting Spacecraft Maximum Allowable Concentrations for 1 hour or 24 hour Contingency Exposures to Airborne Chemicals," 22 nd International Conference on Environmental Systems, Technical Paper 921410, Seattle, WA., 1992.

31.7.15)

op. cit., Palmer

31.7.16)

Limero, T., Trowbridge, J., Taraszewski, S., Foster, J., and James, J., "Results of the Risk Mitigation Experiment for the Volatile Organic Analyzer", 28 th International Conference on Environmental Systems, Technical Paper 981745, Danvers, MA., 1998.

31.7.17) Brittain, A., Bass, P., Breach, J., and Limero, T., "Instrumentation for Analyzing Volatile Organic Compounds in Inhabited Enclosed Environments", 30 th International Conference on Environmental Systems, Technical Paper 2000-01-2434, Toulouse, FR., 2000. 31.7.18)

Eiceman, G., Karpas, Z., Ion Mobility Spectrometry, 2 nd edition, CRC Press, Taylor & Francis Group, Boca Raton, Fl. 2005.

31.7.19)

Personal communications: VOA Statement of Work 1992

31.7.20)

Limero, T., Cross, J., Brittain, A., Breach, J., "Selection and Development of GC/IMS Technology to Measure Targeted Volatile Organic Compounds in Spacecraft Habitable Volumes, Proceedings from the 5 th International Workshop on Ion Mobility Spectrometry, Jackson, Wyoming, 1996, ISBN 0-9660915-0-7.

31.7.21)

Limero, T., Reese, E., Trowbridge, Hohman, R., and James, J., "The Volatile Organic Analyzer (VOA) Aboard the International Space Station", Technical Paper 2002-01-2407, 32 nd International Conference on Environmental Systems, San Antonio, TX., 2002.

31.7.22)

op cit., Limero, 1998

31.7.23)

Limero, T., Bollan, H., Brokenshire, J., and Breach, J., "Preliminary Results From a Sea Trial of the Volatile Organic Analyzer", 3 `d Submarine Air Monitoring and Purification Conference, Emden, Germany, 2003.

31.7.24)

Bollan, H., Brokenshire, J., May, I., Breach, J., and Limero, T., "Measurement of Trace Organic Compounds in Submarine Atmospheres", 4 th Submarine Air Monitoring and Purification Conference, Uncasville, CT., 2005.

31.7.25)

Limero, T., Reese, E., "First Operational Use of the ISS-VOA in a Potential Contingency Event," International Journal for the Ion Mobility Spectrometry, 5(2002)3, pp 27-30.

126 of 130


31.7.26)


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Limero, T., "Validation of the Volatile Organic Analyzer (VOA) Aboard the International Space Station, Technical Paper 2003-01-2646, 33 `d International Conference on Environmental Systems, Vancouver, B.C., 2003.

31.7.27)

Limero, T., "Volatile Organic Analyzer (VOA) in 2006: Repair, Revalidation, and Restart of Elektron Event", International Society for Ion Mobility Spectrometry (ISIMS) Conference Proceedings, 2007.

31.7.28) Limero, T., Cheng, P., and Boyd, J., "Preliminary Investigation of Gas ChromatographyDifferential Mobility Spectrometry as a Replacement for the Volatile Organic Analyzer," Proceedings of the 15 th International Workshop for Ion Mobility Spectrometry, Honolulu, HI., 2006. 31.7.29)

Limero, T., "Evaluation of Gas Chromatography-Differential Mobility Spectrometry for the Measurement of Air Contaminants in Spacecraft," 36 th International Conference on Environmental Systems, Technical Paper 2006-01-2153, Norfolk, VA., 2006.

31.7.30)

Limero, T., Reese, E., Cheng, P., "Demonstration of the microAnalyzer's Measurement of Common Trace Volatile Organic Compounds in Spacecraft Atmospheres," Technical Paper 2008-01-2128, 38 th International Conference on Environmental Systems, San Francisco, CA., 2008.

31.7.33)

op cit., Eiceman op cit., Limero, Technical Paper 2006-01-2153 op cit., Limero, Technical Paper 2008-01-2128

31.7.34)

Limero, T., Cheng, P., Reese, E., and Trowbridge, J., "Evaluation of the Air Quality

31.7.31) 31.7.32)

Monitor's Performance in Measuring Volatile Organic Compounds Aboard the International Space Station," 6th Submarine Air Monitoring Air Purification Conference, San Diego, CA., 2009. 31.7.35)

ibid., Limero 2009

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31.8.1 Mass Determination of Ions Detected by Bennett Ion rf Mass Spectrometer, Johnson, Charles Y., J. Applied Physics V 29, 740-741, 1958. 31.8.2 Small Double Focusing Mass spectrometer, Nier, A. O., Rev. Sci. Inst., 31, 1127-2232, 1960.

31.9.1 Ion Mass Spectrometer on the Explorer XXXI Satellite, Hoffman, J. H., Proceedings of the IEEE, 57, No. 6, 1063-1067. 1969. 31.9.2 Studies of the Composition of the Ionosphere with a Magnetic Deflection Mass spectrometer, Hoffman, J. H., Int. J. Mass Spectrometry and Ion Physics, 4, 315-322, 1970 31.9.3 Initial ion Composition Results from the Isis — 2 Satellite, Hoffman J. H., W. H. Dodson, C. R. Lippincott, H. D. Hammack, J. Geophys. Res. 79, 4246-4261, 1974.

31.10.1 Lunar Orbital Mass Spectrometer Experiment, Hoffman, J. H., R. R. Hodges, and D. E. Evans, Apollo 15 Preliminary Science Report, Sect. 19, NASA SP-289, 1972. 31.10.2 Absolute Calibration of Apollo Lunar Orbital Mass spectrometer, Yeager, P., Smith, A., Jackson, J. J., Hoffman, J. H., J Vac. Sci, 1972 31.10.3 Lunar Atmospheric Composition Experiment, Hoffman, J. H., Hodges, R. R., Johnson, F. S. and Evans, D. E., Apollo 17 Preliminary Science Report, Sect. 17, NASA SP-

31.11.1 The magnetic ion mass spectrometer on Atmospheric Explorer, Hoffman, W. B. Hanson, and C. R. Lippincott, Radio Science, 8, No. 4, 315-322, 1973. 31.11.2 The Bennett ion-mass spectrometer on Atmospheric Explorer C and E, Brinton, H. C., L. R. Scott, M. W. Pharo III, and J. T. C. Coulson, Radio Science, 8, No. 4, 323-332, 1973. 31.11.3 The open source neutral mass spectrometer on Atmospheric Explorer C, D, and E, Nier, A. O., W. E. Potter, D. R. Hickman and K. Mauersberger, Radio Science, 8, No. 4, 271-276, 1973. 31.11.4 A neutral-atmosphere composition experiment Atmospheric Explorer C, D, and E, Pelz, Davit T., Carl A. Reber, Alan E. Heden, and George R. Carignan, Radio Science, 8, No. 4, 277-283, 1973.

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31.12.1 Pioneer Venus Sounder Probe Neutral Mass Spectrometer, IEEE Transactions on Geoscience and Remote Sensing, GE-18, No. 1, 80-84, 1980. 31.12.2 The Pioneer Venus Bus Neutral Gas Mass Spectrometer, IEEE Transactions on Geoscience and Remote Sensing, GE-18, No. 1, 122-125, 1980. 31.12.3 The Measurement of Chemically Reactive Atmospheric Constituents by Mass spectrometers Carried on High Speed Spacecraft, Nier, A. O., W. E. Potter, D, C. Kayser, and R. G. Finstad, Geophys. Res. Lett.,l, 197, 1074. 31.12.4 Bennett Ion Mass Spectrometers on the Pioneer Venus Bus and Orbiter, Taylor, H. A, Jr. H. C. Brinton, T. C. G. Wagner, B. H. Blackwell, and G. R. Cordier, IEEE Transactions on Geoscience and Remote Sensing, GE-18, No. 1, 44-48, 1980. 31.12.5 Pioneer Venus Orbiter Neutral Gas Mass Spectrometer Experiment, Niemann, H. B., J. R. Booth, J. E. Cooley, R. E. Hartle, W. T. Kasprzak, N. W. Spenser, S. H. Way, D. M. Hunten, and G. R. Carignan, IEEE Transactions on Geoscience and Remote Sensing, GE-18, No. 1, 60-64, 1980.

31.13.1 Phoenix Mars Mission — The Thermal Evolved Gas Analyzer, Hoffman, John H., Roy. C. Chaney, and Hilton Hammack, J. of the Am. Soc. for Mass Spectrometry, 19, No. 10,1377-1381, 2008.

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31.15 Acronyms

Ar

argon

CO2

carbon dioxide

He

helium

HGDL

Hazard and Gas Detection Lab

min

minute

MS

mass spectrometer

N2

nitrogen

ppm

part per million

psig

pound per square inch gauge

sccm

standard cubic centimeter per minute

sccs

standard cubic centimeter per second

scf

standard cubic feet

sec

second

sLpm

standard liter per minute

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